RPM revision for Fedora

Simplify RPM version and release creation.  I have borrowed the
scheme used by Oz instead of our current technique based on git
describe.  The Oz scheme uses a time stamp which generally helps
avoid problems with version ordering.

Remove the mock plugins from the default RPM build.  They remain
in setup.py and can be built as RPMs by setting the %{build_mock}
macro, which remains the default behavior of the upstream
Makefile.  This avoids having the testing packages built when
using koji.