`gotestsum` has user friendlier output that emits final summary, also it can emit junit xml file for
automated analysis instead of current format that should significantly
ease automated analysis of CI.

The environment variables needed for envoking `rkt` command line
should include host PATH (to access `iptables`).

Given that the command runs outside the VM, untrusted task environment
variables should NOT be honored here.

We do this already with `rkt`, but the change is quite subtle to miss
when refactoring.

Fix flakiness in docker tests

The assertion here is causing many spurious failures that aren't
actually relevant to the test itself.

We are tracking the cause for this failure independently, and it would
make more sense to have a dedicated test for clean shutdown.

We already have two other Kill tests (e.g.
TestDockerDriver_Start_Kill_Wait and
TestDockerDriver_Start_KillTimeout), so don't need yet another flaky
test.

Noticed an issue in Docker daemon failing to handle the OOM test case
failure in build https://travis-ci.org/hashicorp/nomad/jobs/468027848 ,
and I suspect it's related to the process dying so quickly, and
potentially the way we are starting the task, so added a start up delay
and made it more consistent with other tests that don't seem as flaky.

The following is the log line showing Docker returning 500 error condition; while we can probably handle it gracefully without retrying, the retry is very cheap in this case and it's more of an optimization that we can handle in follow up PR.

```
    testlog.go:32: 2018-12-14T14:57:52.626Z [DEBUG] docker/driver.go:852: docker: setting container startup command: task_name=nc-demo command="/bin/nc -l 127.0.0.1 -p 0"
    testlog.go:32: 2018-12-14T14:57:52.626Z [DEBUG] docker/driver.go:866: docker: setting container name: task_name=nc-demo container_name=724a3e77-8b15-e657-f6aa-84c2d3243b18
    testlog.go:32: 2018-12-14T14:57:52.694Z [INFO ] docker/driver.go:196: docker: created container: container_id=362b6ea183f3c4ce472d7d7571ca47023cea1df0f5eb920827921716f17718be
    testlog.go:32: 2018-12-14T14:57:53.523Z [DEBUG] docker/driver.go:416: docker: failed to start container: container_id=362b6ea183f3c4ce472d7d7571ca47023cea1df0f5eb920827921716f17718be attempt=1 error="API error (500): {"message":"cannot start a stopped process: unknown"}
        "
    testlog.go:32: 2018-12-14T14:57:55.394Z [DEBUG] docker/driver.go:416: docker: failed to start container: container_id=362b6ea183f3c4ce472d7d7571ca47023cea1df0f5eb920827921716f17718be attempt=2 error="API error (500): {"message":"cannot start a stopped process: unknown"}
        "
    testlog.go:32: 2018-12-14T14:57:57.243Z [DEBUG] docker/driver.go:416: docker: failed to start container: container_id=362b6ea183f3c4ce472d7d7571ca47023cea1df0f5eb920827921716f17718be attempt=3 error="API error (500): {"message":"cannot start a stopped process: unknown"}
        "
```

Using `:latest` tag is typically a cause of pain, as underlying image
changes behavior.  Here, I'm switching to using a point release, and
re-updating the stored tarballs with it.

Sadly, when saving/loading images, the repo digeset is not supported:
https://github.com/moby/moby/issues/22011 ; but using point releases
should mitigate the problem.

The motivation here is that docker tests have some flakiness due to
accidental importing of `busybox:latest` which has `/bin/nc` that no
longer supports `-p 0`:

```
$ docker run -it --rm busybox /bin/nc -l 127.0.0.1 -p 0
Unable to find image 'busybox:latest' locally
latest: Pulling from library/busybox
Digest: sha256:2a03a6059f21e150ae84b0973863609494aad70f0a80eaeb64bddd8d92465812
Status: Downloaded newer image for busybox:latest
nc: bad local port '0'
```

Looks like older busybox versions (e.g. `busybox:1.24` do honor `-p 0`
as the test expect, but I would rather update busybox to fix.

GRPC Executor

Upgrade to Golang 1.11.3

workaround a regression in 1.11.3

> We are aware of a functionality regression in "go get" when executed in GOPATH mode on an import path pattern containing "..." (e.g., "go get github.com/golang/pkg/..."), when downloading packages not already present in the GOPATH workspace. This is issue golang.org/issue/29241. It will be resolved in the next minor patch releases, Go 1.11.4 and Go 1.10.7, which we plan to release soon. We apologize for any disruption.

* master: (71 commits)
  Fix output of 'nomad deployment fail' with no arg
  Always create a running allocation when testing task state
  tests: ensure exec tests pass valid task resources (#4992)
  some changes for more idiomatic code
  fix iops related tests
  fixed bug in loop delay
  gofmt
  improved code for readability
  client: updateAlloc release lock after read
  fixup! device attributes in `nomad node status -verbose`
  drivers/exec: support device binds and mounts
  fix iops bug and increase test matrix coverage
  tests: tag image explicitly
  changelog
  ci: install lxc-templates explicitly
  tests: skip checking rdma cgroup
  ci: use Ubuntu 16.04 (Xenial) in TravisCI
  client: update driver info on new fingerprint
  drivers/docker: enforce volumes.enabled (#4983)
  client: Style: use fluent style for building loggers
  ...

Fix output of 'nomad deployment fail' with no arg

UI: Fix intermittent test failure "cannot read property name of undefined"

client: updateAlloc release lock after read

Prior to 97f33bb1, executor cgroup validation errors were
silently ignored.  Enforcing them reveals test cases that missed them.

This doesn't change customer facing contract, as resource struct is
is either configured or we default to 100 (much higher than 2).

rpc accept loop: added backoff on logging

Display device attributes in `nomad node status -verbose`

Make alloc health watcher a postrun hook rather than shutdown hook

The allocLock is used to synchronize access to the alloc runner map, not
to ensure internal consistency of the alloc runners themselves. This
updates the updateAlloc process to avoid hanging on to an exclusive lock
of the map while applying changes to allocrunners themselves, as they
should be internally consistent.

This fixes a bug where any client allocation api will block during the
shutdown or updating of an allocrunner and its child taskrunners.

drivers/exec: Support devices mounts

Device preemption

fix iops bug and increase test matrix coverage

client: update driver info on new driver fingerprint