Add glob pattern support to gossfile

[AlexandreCarlton]

In order to add easily add tests to an existing goss suite it would be great if the gossfile feature supported the use of glob patterns. This could be used to specify all files in a folder when running a test suite:

gossfile:
  goss_*.yaml: {}

Instead of manually having to append filenames to the main goss file, we could merely drop in a file matching the goss_*.yaml pattern and be on our merry way.