extract-files: Bring back old behavior for SRC

* Previously, you could just specify a SRC directly
  after './extract-files', and it would work, but
  now, the arg '-p/--path' is required for the same
  behavior to be applied for the extraction
* Add a catch-all case that just sets SRC if the arg
  doesn't match any of the args that we care about
* Make the ordering of the cases alphabetical

Change-Id: Ia2ad42d444904ead6b3bd6d910af363eb7f015cc