This PR removes locking around commonly accessed node attributes that do
not need to be locked. The locking could cause nodes to TTL as the
heartbeat code path was acquiring a lock that could be held for an
excessively long time. An example of this is when Vault is inaccessible,
since the fingerprint is run with a lock held but the Vault
fingerprinter makes the API calls with a large timeout.

Fixes https://github.com/hashicorp/nomad/issues/2689

Fix panic in emitting tagged allocation metrics

Add ability to reset ACL bootstrap process

Hide non-user commands from autocomplete output

Fix MemorySwappiness on Windows Docker

Fix docker user specified syslogging

Add elsevier-core-engineering/replicator to community page.

Fixes https://github.com/hashicorp/nomad/issues/3181

Fix invalid CPU stats on Windows

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.

build: Rework Vagrant for multiple operating systems; add FreeBSD support

Expand TLS upgrade guide

This commit reworks the Vagrantfile for Nomad in order to support
straightforward testing on more than one operating system, whilst
retaining the ability to stand up a test cluster running Ubuntu.

The following changes are made:

- Scripts have been extracted from the Vagrantfile into their own shell
  script files, in order that editors lint them.

- All scripts have been edited to lint with no warnings or errors for
  their respective shells.

- Scripts are named according to the operating system and privilege
  level which they run. We prefer to run a whole shell script as root
  versus prefixing (essentially) every command with `sudo` or an
  equivalent.

- The Linux development box has been separated from the test cluster,
  removing some of the more gnarly (and less portable) logic. The Linux
  development box is still primary and autostarts.

- A FreeBSD target has been added. The base box works for both
  Virtualbox and VMWare Fusion.

- A target is added to the GNUmakefile to stand up a test cluster, using
  the default provider, or overriding the provider by setting the PROVIDER
  variable in make:
	- `make testcluster`
	- `make testcluster PROVIDER=vmware_fusion`

- Machines in the test cluster have Avahi configured for zeroconf
  discovery. Each machine can ping each other machine at `hostname.local`
  - for example `nomad-server02.local`, `nomad-client03.local`.

The old wording made it sound like verify_https_client=true broke *all*
https health checks.

Current plan for the future still requires two server restarts.

client: Guard against "NaN" values from floats

This commit protects against finding `0.NaN` tokens in JSON streams
because of infinity representation on serialization.

deps: Update golang.org/x/sys/{unix,windows}

This PR hides non-user CLI commands from the list of autocomplete
suggestions.

Sync namespace changes

- Non-trivial clusters risk rescheduling many if not all of their jobs
  if they don't adjust their heartbeat configs.
- Still needs links

Tagged metrics API