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.

Gemfile

@@ -13,6 +13,10 @@ group :development do
   else
     gem 'vagrant', :git => 'https://github.com/mitchellh/vagrant.git'
   end
+
+  gem 'vagrant-spec', :github => 'mitchellh/vagrant-spec',
+    tag: ENV['VAGRANT_SPEC_VERSION'] || "9bba7e1228379c0a249a06ce76ba8ea7d276afbe"
+
   gem 'pry'
 end