Added support for including phantom.js in the cookbook.

Added it to the Berksfile, added a blank package to the default (sine
we're adding nginx already), added it to the metadata.rb.

References #4.
Added phantomjs recipe to kitchen, and test to main_spec

The phantomjs recipe needed to be in .kitchen.yml for the recipe to be
run, and a test was added to determine whether the recipe was run
correctly.

References #4.
Replaced test with one that works!

Checked for presence of actual binary instead of package that doesn't
exist.