(PUP-3014) Accept. tests - 3.7 PMT updates generate

This commit adds additional acceptance test coverage for updates
to the puppet module generate command. These tests validate the
following:

* (PUP-2781) Generated requirements should use the version_requirement field
* (PUP-2691) Generate should succeed when skeletons use the 'description'
  metadata property.
* (PUP-2079) Generate should support erb skeleton templates"