rkt: revert to pre-0.9 --cpu flag

Make driver logging less redundant

logmon: Reattach to existing loggers

Changes logging warnings/errors only if the state changes
from healthy to unhealthy

test: porting TestTaskRunner_SimpleRun_Dispatch

This commit prevents us from creating duplicate logmon hooks when
restoring allocations by persisting the logmon reattach config using
HookData.

Porting test from 0.8 to 0.9.

Nvidia runtime

See
https://github.com/hashicorp/nomad/issues/3394#issuecomment-453296121
for details. During 0.9 development we switched to shares, but we'd
prefer to maintain backward compat.

docs: updated tense around fixed bug

  - docker fingerprint issues a docker api system info call to get the
  list of supported OCI runtimes.
  - OCI runtimes are reported as comma separated list of names
  - docker driver is aware of GPU runtime presence
  - docker driver throws an error when user tries to run container with
  GPU, when GPU runtime is not present
  - docker GPU runtime name is configurable

 - go-dockerclient is updated because of lack of "runtime" API field
 - docker/docker is updated because go-dockerclient depends on docker
 master branch

make change to the 0.8.7 release date

executor: Always close stdout/stderr fifos

docker: Terminate dockerlogger

Port a bunch of pre-0.9 Consul tests to 0.9

propagate logs to executor plugin

Previously, we did not attempt to stop Docker Logger processes until
DestroyTask, which means that under many circumstances, we will never
successfully close the plugin client.

This commit terminates the plugin process when `run` terminates, or when
`DestroyTask` is called.

Steps to repro:

```
$ nomad agent -dev
$ nomad init
$ nomad run example.nomad
$ nomad stop example
$ ps aux | grep nomad # See docker logger process running
$ signal the dev agent
$ ps aux | grep nomad # See docker logger process running
```

Plugins use parent loggers

executor: streaming stats api

Skipping a failing one as I need to move to some other work and don't
want to leave this work orphaned on my machine.

Ported from pre-0.9 tests.

Restore a pre-0.9 test that asserts Consul services are deregistered
before a task's shutdown delay.

Co-Authored-By: nickethier <ncethier@gmail.com>

use t.Logf instead of fmt.Printf
Co-Authored-By: nickethier <ncethier@gmail.com>

plugins/driver: update driver interface to support streaming stats

client/tr: use streaming stats api

TODO:
 * how to handle errors and closed channel during stats streaming
 * prevent tight loop if Stats(ctx) returns an error

drivers: update drivers TaskStats RPC to handle streaming results

executor: better error handling in stats rpc

docker: better control and error handling of stats rpc

driver: allow stats to return a recoverable error