Add rudimentary spec test to WaitTillUp using vagrant-spec

Add some basic spec tests for the WaitTillUp action class to lay some
foundations. Utilize vagrant-spec pinned to a known working commit for
tests to pass consistently until they provide releases.

Requires updating some of the rspec libraries and includes
sharedcontext.rb from the jantman/vagrant-r10k project on github.

spec/spec_helper.rb

@@ -1,5 +1,6 @@
 require 'vagrant-libvirt'
 require 'support/environment_helper'
+require 'vagrant-spec/unit'
 
 RSpec.configure do |spec|
 end