Py2RPM helper: always return all names from conversion

Many parts of anvil rely on the fact that convert_names_to_rpm returns
same number of rpms names and in same order as it was given. This change
ensures that this is the case.

Change-Id: Id6107f8b8558be52d531d413e44325c8fb031371
Filter out components not listed in origins file

If component is not mentioned in origins file (like oslo-messaging in
havana-1) this means it is not needed for this origins and it should
be ignored.

Change-Id: I8ce113bd823d6a3d3f1c743b30585af79966720e