Create an RPM spec file for buildsome under CentOS 7

The buildsome-deps provides the build-time dependencies and is
constructed differently.

Using 'mock', building the RPM is done using a single command:

    ./packaging/build-srpm -i buildsome -o . -m <DIST>

Where DIST is the name of the mock configuration.
Force Version.hs to always recompile
Lib/Version - use git describe with -dirty and short SHA for nicer version