Mount Devices in container based drivers

Re-enable Client GC tests

Fix docker driver tests

deviceDir is used for specifying mount/device host paths, and those
should be absolute paths.

Also, LXC requires target paths to be relative.  Container paths in LXC
binds should never be absolute paths, so we strip any preceeding `/`,
even if a user sets one.

UI: Keep line charts in their canvases at all times

The previous integration test was broken during the client refactor, and
it seems to be some sort of race with state updating.

I'm going to try and construct a replacement test as part of work on
performance, but for now, the underlying behaviour is still being
tested.

Fix various bugs with task events

Fixes the following:
* Emitting events when the task fails to start
* Don't double emit events on task shutdown (nomad stop)
* Don't emit a OOM kill metric unless actually OOM'd

server/vault: Lock Vault expiration tracking

tests: fix rkt tests

The rkt command itself needs an environment with PATH set to find iptables.

Add guards around subtracting summary count

Also update the new recommended `nomad job` subcommands

* Add Nomad RA

* Add deployment guide and nav

* Deployment Guide update

* Minor typo fixes

* Update diagrams

* Fixes for review

* Link fixes and typo fix

* Edits following review

- Update image text from "zone" to "datacenter" to match Nomad terminology
- Clean up text based on Preetha's feedback

* Text updates

Based on feedback from Rob

* Update diagrams

* fixing spelling

* Add suggestions from Preetha and Omar

WaitForResult expects body to fail and retries few times before giving
up.  Assertions inside the testfn body causes it to terminate abruptly
without retrying.

`currentExpiration` field is accessed in multiple goroutines: Stats and
renewal, so needs locking.

I don't anticipate high contention, so simple mutex suffices.

When `t.Parallel()` is used inside a `t.Run()` sub-set, the closure
doesn't behave as expected, and some cases effectively get skipped.
More details can be found in
https://gist.github.com/posener/92a55c4cd441fc5e5e85f27bca008721

Some tests have containers that die almost immediately, and may die
and cleaned up before `driver.WaitUntilStarted` runs.

The causes for container dying seems special for each test:
* TestDockerDriver_Cleanup: `hello-world` image just emits a message and exits immediately
* TestDockerDriver_ForcePull_RepoDigest: the busybox image in `TestDockerDriver_ForcePull_RepoDigest` test didn't support `-p 0` argument
* TestDockerDriver_Entrypoint: with the entrypoint being `/bin/sh -c`, the command needs to be the entire string; otherwise, it ignores the comments

Third Party Driver Plugins Support

no need to double the work

libcontainer already manages `/dev`, overriding task_dir - so let's use it for `/proc` as well and remove deadcode.

this allows us to drop a cyclical import, but is subobptimal as it
requires BaseDriver tests to move. This falls firmly into the realm of
being a hack. Alternatives welcome.

This removes a cyclical dependency when importing client/structs from
dependencies of the plugin_loader, specifically, drivers. Due to
client/config also depending on the plugin_loader.

It also better reflects the ownership of fingerprint structs, as they
are fairly internal to the fingerprint manager.