(Maint) Fix up the get_module_path parser function

(Maint) Fix up the get_module_path parser function

This patch switches the spec tests for the get_module_path function to
use mock objects.  The underlying Puppet::Module.find method has
reasonable test coverage inside of Puppet core so we might as well break
the tight dependency while we're fixing up the specs to use the new
parser scope.

The behavior of the parser function itself should still have complete
coverage even though the tests have switched to mock the implementation
inside of Puppet.