Skarmark applicability perf improvements

1. updated get_repo_units conduit method to request only the required unit association data resulting in 65% performance improvement for applicability and much better memory footprint.
2. performance improvements to ApplicabilityRegenerationManager to avoid multiple calls per consumer for retrieving profiles and bound repos.
3. updated repo applicability regeneration to check only existing RepoProfileApplicability objects instead of creating new objects when needed.