Adds an execption type (inherits from TypeError) for the ways
arguments to Butler.pruneCollections can fail. This allows the
CLI script function to catch the exception, know the reason for
the failure, and format a message to report the error in a way
that will make sense on the command line.
If this seems like an acceptible solution to reviewers this pattern
may be used elsewhere to improve CLI error reporting as needed.

Adds various ways of formatting the collections.

Puts duplicated test repo code for the various CLI tests in a
shared location & adds some API for modifying the repo.

Numpy recently added a deprecation warning for "ragged" arrays;
in this case it was ragged because of a type mismatch;
CollectionSearch vs str. Making the CollectionSearch a string
in the list comprehension prevents us from encountering the
warning.

removes use of @patch, and just replaces mocked functions.