More comments + stable & defined op sorting order

Add more comments to multipip explaining how the
ranking/scoring function works, and rename the logger
to denote that it's really a constant global value and
sort the operators (when versions are found to be
the same) in a explictly defined order (instead of the
more implicit sort order previously).

Change-Id: I948ee78367facbfcd1c593b1b0844ca5230a8bd5