Currently, libcontainer-based executor, upon shutdown, kills the
container initial process.  The children of the killed process remain
running, and the executor is never marked as terminated until they do.

Also, fix a case where we treat processes as successful, when
`proc.Wait()` fails.  In some attempts, I was getting "waitid no child
processes" errors and such error shouldn't get process to be considered
successful.

Ensure that exec children processes get killed as well.

Batch update for the PRs I recently merged.

Refactor and repackage client/driver

Use user provided image name to launch container

Support bind and tmpfs docker mounts

Co-Authored-By: notnoop <mahmood@notnoop.com>

With the introduction of driver plugins, we're temporarily relying on
_run time validation_ of driver configurations, rather than submission
time.

The logging package is used by logmon and the legacy mock_driver. Because the
legacy drivers are going away, I'm moving it here to signify its actual
ownership.

This creates a drivers/shared/structs package and moves the buffer size
checks into it.

As part of deprecating legacy drivers, we're moving the env package to a
new drivers/shared tree, as it is used by the modern docker and rkt
driver packages, and is useful for 3rd party plugins.

Port metric prefix filtering to master

make: Fix invocation of vault e2e test

vault: protect against empty Vault secret response

Fixes #4921

Sadly, we don't have proper mechanism to mock Vault client, so not sure how to best test this.

I inspected the Vault client interactions, specially for cases where returned value is nil even if the error is also nil.  I believe we covered all correctly now:
* [`v.client.Sys().InitStatus()`](https://github.com/hashicorp/nomad/blob/f3853f11daa51336a2d46d883b1aff6feeddc7ec/nomad/vault.go#L427) - the value is non-nil boolean
* [`v.client.Sys().CapabilitiesSelf(path)`](https://github.com/hashicorp/nomad/blob/f3853f11daa51336a2d46d883b1aff6feeddc7ec/nomad/vault.go#L812): Capabilities handles empty bodies in [`hasCapability`](https://github.com/hashicorp/nomad/blob/f3853f11daa51336a2d46d883b1aff6feeddc7ec/vendor/github.com/hashicorp/vault/api/sys_capabilities.go#L43-L45) - also the `nil` array is handled with proper fail-safe default.
* [`v.client.Logical().Read(fmt.Sprintf("auth/token/roles/%s", role))`](https://github.com/hashicorp/nomad/blob/f3853f11daa51336a2d46d883b1aff6feeddc7ec/nomad/vault.go#L834-L840) handles when `rsecret` is nil

Also, fix a case where a successful second attempt of loading token can
cause a panic.

change to testing utilities to fix rkt tests

add generic plugin manager interface and orchestration

testing: in MkAllocDir, do not update TaskConfig with All() from the task builder, just with Env() (because it pollutes environment variables with node attributes and fails the rkt tests)

Modify fingerprint interface to use typed attribute struct

Device hook and devices affect computed node class