Fix hit categories to get correct hit efficiency

Use the Velo category for hit efficiency checking.

This should solve the problem observed with low hit efficiency in the allen_gaudi_velo.py test.

@cagapopo @dcampora As discussed in person and on mattermost. Is this test actually run as part of the nightlies?

f222aa1c refactors the script and adds a qmtest. The test runs PrChecker to get the tracking efficiency of Velo tracks from GaudiAllen.