Makefile: Remove queueing script for repository database updates
Makefile: Create SRPM repository metadata after all SRPMS are created

It is not necessary to rebuild the SRPM repository metadata
after each SRPM is built.   Build it once, at the end.

Signed-off-by: Euan Harris <euan.harris@citrix.com>
Makefile: Add documentation

Signed-off-by: Euan Harris <euan.harris@citrix.com>
Merge pull request #542 from euanh/atomic-createrepo

Remove createrepo queueing script