Also install new porter dep

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...

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

This reverts commit 9f2ea928.