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

Handle client initialization errors when adding/restoring allocs

Co-Authored-By: preetapan <preetha@hashicorp.com>

Added a unit test with custom statedb implementation that errors, to
use to verify destroy errors

Also modify restore such that any handled errors don't propagate
back to the client

Restore currently shuts down the client so the alloc update cant
always make it to the server

We mark the alloc as failed and track failed allocs so that we don't send
updates after the first time

client: Cleanup allocrunner access