Add support for componentized USER spec file

CPACK_RPM_USER_BINARY_SPECFILE can now be specified on a per-component
basis using CPACK_RPM_<componentName>_USER_BINARY_SPECFILE.

Inspired-By: Theodore Papadopoulo with its patch proposal.
Merge topic 'CPackRPM-componentizedUserSpecFile' into next

2ef908f Add support for componentized USER spec file