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

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 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

`distinct_property` constraint

Add metrics to show allocations on the client

Round two of env var cleaning

deps: Update github.com/mitchellh/go-ps

This PR adds the following metrics to the client:
client.allocations.migrating
client.allocations.blocked
client.allocations.pending
client.allocations.running
client.allocations.terminal

Also adds some missing fields to the API version of the evaluation.

This commit adds Solaris versions of the following functions:

- `linkDir`
- `unlinkDir`
- `createSecretDir`
- `removeSecretDir`

I believe this requires Go 1.8 in order to compile, as the unlink
syscall was previously missing.

This update pulls in a commit adding support for Solaris.

Correct error message re length of service name

Remove duplicate check

Website: Add Mega Nav

Should bring us into conformance with IEEE Std 1003.1, 2004 Edition:
http://pubs.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap08.html

1 alloc/op and ~80ns/op on my machine.