We were just emitting Killed/Terminated events before. In v0.8 we
emitted Killing/Killed, but lacked Terminated when explicitly stopping
a task. This change makes it so Terminated is always included, whether
explicitly stopping a task or it exiting on its own.

New output:

2019-01-04T14:58:51-08:00  Killed            Task successfully killed
2019-01-04T14:58:51-08:00  Terminated        Exit Code: 130, Signal: 2
2019-01-04T14:58:51-08:00  Killing           Sent interrupt
2019-01-04T14:58:51-08:00  Leader Task Dead  Leader Task in Group dead
2019-01-04T14:58:49-08:00  Started           Task started by client
2019-01-04T14:58:49-08:00  Task Setup        Building Task Directory
2019-01-04T14:58:49-08:00  Received          Task received by client

Old (v0.8.6) output:

2019-01-04T22:14:54Z  Killed            Task successfully killed
2019-01-04T22:14:54Z  Killing           Sent interrupt. Waiting 5s before force killing
2019-01-04T22:14:54Z  Leader Task Dead  Leader Task in Group dead
2019-01-04T22:14:53Z  Started           Task started by client
2019-01-04T22:14:53Z  Task Setup        Building Task Directory
2019-01-04T22:14:53Z  Received          Task received by client

e2e: Output setup instructions after terraform

taskrunner: emit TaskReceived event

Preserve pre-0.9, where task runner emits `Received: Task received by
client` event on task runner creation.

updated to latest hashicorp/raft and hashicorp/memberlist to pull

This adds a message that provides environment setup instructions for
running e2e tests after running terraform apply.

This allows copy/pasting exports, rather than manually constructing
them.

Use a dedicated /dev mount so we can inject more devices if necessary,
and avoid allowing a container to contaminate host /dev.

Follow up to https://github.com/hashicorp/nomad/pull/5143 - and fixes master.

upstream fixes for accept-loop error handling

Restore some `exec` behavior 

WIP: fix failing tests caused by async driver manager

Restores pre-0.9 behavior, where Nomad makes /dev available to exec
task.  Switching to libcontainer, we accidentally made only a small
subset available.

Here, we err on the side of preserving behavior of 0.8, instead of going
for the sensible route, where only a reasonable subset of devices is
mounted by default and user can opt to request more.

libcontainer based drivers (e.g. exec, java) should default to running
processes as `nobody` [1]; but libcontainer treats empty user as `root`
in our case (either because of default or due to `root` being current
user).

[1] https://github.com/hashicorp/nomad/blob/94c28a4c6cc45f1b377d50a6bff2017b46c43d18/website/source/docs/job-specification/task.html.md#task-parameters

allocrunner: Standardised discard logs

taskrunner: Persist environment from hooks

Fix `make check`

Follow up from https://github.com/hashicorp/nomad/pull/5007#pullrequestreview-186739124

drivers: Cleanup root user fingerprinting

https://github.com/hashicorp/nomad/pull/5032 introduced a regression
where the origHookState was used in place of the response from the hook.

e2e tests for spread stanza

Store device envs separately and pass to drivers

client: add proper build flag to allocrunner testing.go