Port some 0.8.7 alloc runner tests

Created .github; Added CoC

Set NextEval when making `failed-follow-up` evals

When Vault token expires and task is restarted, emit `TaskRestartSignal`
similar to v0.8.7

From https://github.com/hashicorp/nomad/blob/v0.8.7/client/task_runner_test.go#L1427

From https://github.com/hashicorp/nomad/blob/v0.8.7/client/task_runner_test.go#L1352

From https://github.com/hashicorp/nomad/blob/v0.8.7/client/task_runner_test.go#L620

From https://github.com/hashicorp/nomad/blob/v0.8.7/client/task_runner_test.go#L1275

From https://github.com/hashicorp/nomad/blob/v0.8.7/client/task_runner_test.go#L1195

Port TestAllocRunner_RetryArtifact from https://github.com/hashicorp/nomad/blob/v0.8.7/client/alloc_runner_test.go#L610-L672

I changed the test name because it doesn't actually test that artifact
hooks is retried

Support json logging for CLI output for agent 

* caller should created eval id
* prev/next eval used in failed-follow-up

Do not wrap errors from StartTask as that loses Recoverable

Fixes restarting on recoverable errors from StartTask.

Ports TestTaskRunner_Run_RecoverableStartError from 0.8 which discovered
the bug.

Fix regression by restarting on artifact download errors

* reformat lxc guide

* reformat lxc guide

docs: clarify use of toJSON for passwords

Run Docker tests in Windows AppVeyor CI

Fixes #5347

This allows users to locate failed-follow-up evals more easily

docker: Avoid leaking containers during Reattach

tests: port TestAllocRunner_Destroy from 0.8

Also add destroy(ar) helper to fix a bunch of shutdown races in AR
tests.

Currently if a docker_logger cannot be reattached to, we will leak the
container that was being used. This is problematic if e.g using static
ports as it means you can never recover your task, or if a service is
expensive to run and will then be running without supervision.

Track the download status of each artifact independently so that if only
one of many artifacts fails to download, completed artifacts aren't
downloaded again.

Increase resiliency of docker driver logging

Co-Authored-By: dantoml <dani@tomlinson.io>

Sometimes the nomad docker_logger may be killed by a service manager
when restarting the client for upgrades or reliability reasons.

Currently if this happens, we leak the users container and try to
reschedule over it.

This commit adds a new step to the recovery process that will spawn a
new docker logger process that will fetch logs from _the current
timestamp_. This is to avoid restarting users tasks because our logging
sidecar has failed.

0.9.0beta2 contains a regression where artifact download errors would
not cause a task restart and instead immediately fail the task.

This restores the pre-0.9 behavior of retrying all artifact errors and
adds missing tests.

Adds a new helper and removes a duplicated test.

Fix colored terminal output on Windows

Replace IsTravis() references that is intended for more CI environments
rather than for Travis environment specifically.