This fixes a bug related to shutting down of GRPC plugin interfaces
(more info: https://github.com/hashicorp/go-plugin/pull/88)

This does not yet fix all test cases for subprocess leaking, but is a
useful independant change.

test: re-eanble periodic fingerprint test

Test fix races

deps: Update x/net/context

plugins: Shutdown internal plugins

This implements the InternalPluginDriver interface in each driver, and
calls the cancellation fn for their respective eventers.

This fixes a per task goroutine leak during test suite execution.

This allows us to correctly terminate internal state during runs of the
nomad test suite, e.g closing eventer contexts correctly.

This allows std context to be used in place of an x/net/context and
unblocks updating to the latest version of go-plugin.

Task runner recovers from external plugin exiting

fix for user-specified auto-join tags

taskenv: have maps take precedence over primitives

e2e: Add consultemplate test

This adds a basic test for consul template, that verifies the behaviour
of consul-template with task blocking and restarting of tasks

Standardize driver health description messages for all drivers

remove unnecessary logging in rkt driver fingerprint method

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