Build packages for client and yum repositories

As discussed at Madrid workshop.

Fixes #16.
Fixes #17.
As we postponed solving these issues in 14.12, we should be able to rediscuss this now that we have a PR. I agree with @stdweird that we need to address the `externals` repo structure. I don't know what is referred to the "Quattor one" but if it is the one on `quattorsrv.lal.in2p3.fr`, I'd like to see it stopped in favor of one hosted at `yum.quattor.org`. This was only a temporary solution....