executor: streaming stats api

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

Make spread weight a pointer with default value if unset

Re-enable client and java skipped tests

Remove unnecessary usage of alloc.Resource

Docs for spread stanza

Oxford comma in variable interpolation summary

This improves the readability of this section.

WaitForRunning risks a race condition where the allocation succeeds and
completes before WaitForRunning is called (or while it is running).

Here, I made the behavior match the function documentation.

I considered making it stricter, but callers need to account for
allocation terminating immediately after WaitForRunning terminates
anyway.

tests: remove tests for unsupported features

With switching to driver plugins, driver validation is quite tricky and
we need to do some design thinking before supporting it against.

ignore _JAVA_OPTIONS line in `java -version`, as it's relevant.