F arm misc

This PR:
* Uses Go 1.8 executable lookup
* Stores any err message from stats init method
* Allows overriding of Cpu Compute for hosts where it can't be detected

Limit parallelism during garbage collection

Replace `_` with `-` in task names for rkt volumes

Skip inplace update on terminal batch allocation

Fix #2445

Close #2445 - typo in docs

[needs testing] make bin creates a release binary for the host arch

deps: Update github.com/shirou/gopsutil

Return AgentSelf struct from Agent.Self() instead of map

deps: Update github.com/docker/docker/pkg/system

Add NOMAD_{IP,PORT}_<task>_<label> env vars

This commit updates the `system` package of `docker/docker`.

This commit updates `gopsutil` to the latest version, which includes CPU
info support for Illumos.

Handle git ssh artifacts

Eval GC will collect allocs from stopped batch job

Distinct Property Docs and Validation

Direct to master given the trivial change.

This PR skips adding an inplace update to a successfully terminal batch
job to the plan. This avoids extra data in the plan and avoids
triggering updates on all clients that have the terminal allocation.
This is matching behavior of the service scheduler.

/cc @armon for review

This PR fixes a bug in which allocations from stopped batch jobs could
not be garbage collected.

This PR adds handling for downloading git artifacts using ssh with the
format git@github.com:hashicorp/go-getter.git

Fixes https://github.com/hashicorp/nomad/issues/2430

client/allocdir: Add missing functions on Solaris

Added docs for the collection_interval option in the telemetry block