This PR fixes an issue introduced in Nomad 0.6.0 due to
https://github.com/shirou/gopsutil/issues/420. The issue arised from the
fact that the Windows stats from gopsutil reports CPUs in
percentages where we expected ticks.

Always purge stopped containers

Fix repo name passed to docker credential helpers

Update go-getter

* Vendor consul-template

Fixes https://github.com/hashicorp/nomad/issues/3133

* changelog

This PR fixes the server url passed to docker credential helpers and
fixes stderr capture.

Fixes https://github.com/hashicorp/nomad/issues/2957

Fixes https://github.com/hashicorp/nomad/issues/3154

Integration test for round tripping a job.

* Parse Docker mounts correctly

This PR fixes the parsing of Docker mounts and adds testing to ensure no
regressions.

Fixes https://github.com/hashicorp/nomad/issues/3156

* Review feedback

Add support for tagged metrics

Initial ACL enforcement framework