Support alternative cvmfs-config packages

[natefoo]

The cvmfs package depends on a package providing cvmfs-config, which in the default case is provided by the cvmfs-config-default package. This package includes the cvmfs-config.cern.ch repo as the config repo. For Galaxy purposes this is an unnecessary mount - it doesn't harm anything, but for installations that don't use the CERN and OSG repos, you can just install the cvmfs-config-none package, which provides cvmfs-config but with a blank config.

However, cvmfs-config-none is not in the standard cernvm yum repo since you can't have two packages providing the same thing in a single repo, but it is in the (shipped with the repo config but disabled by default) cernvm-config repo. So the following works:

yum install --enablerepo=cernvm-config cvmfs-config-none cvmfs

There are also packages here: http://ecsft.cern.ch/dist/cvmfs/cvmfs-config/, including a Debian package which does the same for Debian-based distros.