Gets us one step closer to a reproducible build. Also removes the unused
vendored version.

`travis.sh` contained some bash-ism despite it being invoked with `sh`.

`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.

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.

Lowering the runtime here to pre 7ca535aa expectations.

The longest package at the time `client/driver` shrunk significantly,
and now the longest packages take less than 5 minutes.

We do have some long running timed out projects due to a stuck shutdown,
but in completed jobs (though they failed), the longest packages took
less than 5 minutes.  The longest running packages in
https://travis-ci.org/hashicorp/nomad/jobs/464640776 were:

```
FAIL  github.com/hashicorp/nomad/nomad                                   268.089s
ok    github.com/hashicorp/nomad/drivers/docker                          203.903s  coverage:  68.8%   of  statements
ok    github.com/hashicorp/nomad/drivers/rkt                             132.104s  coverage:  65.0%   of  statements
ok    github.com/hashicorp/nomad/api                                     123.193s  coverage:  62.9%   of  statements
ok    github.com/hashicorp/nomad/command/agent                           74.657s  ...

nomad/client take very long and exceed 15m sometimes:

In https://travis-ci.org/hashicorp/nomad/jobs/452990197 :

```
panic: test timed out after 15m0s

goroutine 4739 [running]:
testing.(*M).startAlarm.func1()
	/home/travis/.gimme/versions/go1.11.2.linux.amd64/src/testing/testing.go:1296 +0xfd
....
goroutine 4665 [select]:
github.com/hashicorp/nomad/vendor/google.golang.org/grpc.newClientStream.func5(0xc0003dd500, 0xc000420120, 0x2b3f86295588, 0xc000496810)
	/home/travis/gopath/src/github.com/hashicorp/nomad/vendor/google.golang.org/grpc/stream.go:287 +0xd7
created by github.com/hashicorp/nomad/vendor/google.golang.org/grpc.newClientStream
	/home/travis/gopath/src/github.com/hashicorp/nomad/vendor/google.golang.org/grpc/stream.go:286 +0x842
FAIL	github.com/hashicorp/nomad/client/driver	900.036s
```

Introduce a device manager that manages the lifecycle of device plugins
on the client. It fingerprints, collects stats, and forwards Reserve
requests to the correct plugin. The manager, also handles device plugins
failing and validates their output.

Allow it to fail for now with the goal of making it the default build in
the future.

Remove the NOMAD_TEST_RKT flag as a guard for rkt tests. Still require
Linux, root, and rkt to be installed. Only check for rkt installation
once in hopes of speeding up rkt tests a bit.

`make release` and `make prerelease` set a `release` tag to disable
enabling the `mock_driver`

Broke due to a change in go-bindata-assetfs

We make a HashiCorp hard fork of the jteeuwen/go-bindata hard fork that
was replaced and diffed the code against a Dec 1, 2015 copy of the
original repository we had as a cross-check of that hard fork.

This replaces references to jteeuwen/go-bindata to point to the
HashiCorp fork.