Add the Nomad agent version to the node-status CLI output.

build: Replace shell scripts with GNUmakefile

Placing allocs counts towards placement limit

Add deployments to search api

add docs for mount

This PR makes placing new allocations count towards the limit. We do not
restrict how many new placements are made by the limit but we still
count towards the limit. This has the nice affect that if you have a
group with count = 5 and max_parallel = 1 but only 3 allocs exist for it
and a change is made, you will create 2 more at the new version but not
destroy one, taking you down to two running as you would have
previously.

Fixes https://github.com/hashicorp/nomad/issues/3053

Minor doc updates

Update gopsutil to stop calling SetEnv

Minor documentation tweaks

Add Header and Method support for HTTP checks

This commit replaces the shell script-driven build process for Nomad
with one based around GNU Make (note we _do_ use GNU-specific
constructs), requiring no additional scripts for common cases of
development. The following targets are implemented:

Per-OS/arch combinations:

    Binaries (Host - Mac OS X):
	pkg/darwin_amd64/nomad

    Binaries (Host - Linux):
	pkg/linux_386/nomad
	pkg/linux_amd64/nomad
	pkg/linux_amd64-lxc/nomad
	pkg/linux_arm/nomad
	pkg/linux_arm64/nomad
	pkg/windows_386/nomad
	pkg/windows_amd64/nomad

    Packages (Host - Mac OS X):
	pkg/darwin_amd64.zip

    Packages (Host - Linux):
	pkg/linux_386.zip
	pkg/linux_amd64.zip
	pkg/linux_amd64-lxc.zip
	pkg/linux_arm.zip
	pkg/linux_arm64.zip
	pkg/windows_386.zip
	pkg/windows_amd64.zip

Phony targets:

	dev - Builds for the current host GOOS/GOARCH (unless overriden
	      in the environment)

	release - Builds all appropriate release packages for the
	          current host GOOS/GOARCH (i.e. Windows and Linux
		  packages on a Linux host, Darwin packages on an OSX
		  host)

	generate - Generate code for the current host architecture using
	           `go generate`.

	test - Runs the Nomad test suite

	clean - Removes build artifacts

	travis - Runs `make test` with the wrapper script to prevent
	         Travis CI from timing out.

	help - Displays usage information about commonly used targets.

Note that there are some semantic differences from the previous version.

1. `generate` is no longer a dependency of `dev` builds. This is because
   it causes a rebuild every time, even when no code has changed, since
   `go generate` does not appear to leave file timestamps alone.
   Regardless, it is insufficient to generate on one host OS - it needs
   to be run on each target to ensure everything is generated correctly.

2. `gofmt` is no longer checked. This should be enabled as a linter once
   the `gofmt -s` refactoring will pass on the whole code base, in order
   to avoid special cased checks versus using go-metalinter.

Example Usages:

Make a development build for the current GOOS/GOARCH:

	make dev

Make release build packages appropriate for the host OS:

	make release

Update generated code for the host OS:

	make generate

Run linting checks:

	make check

Build a specific alternative GOOS/GOARCH/tags combination:

	make pkg/linux_amd64-pkg/nomad
	make pkg/linux_amd64-pkg.zip

Expose docker mount options