Need convenient way to mount cvmfs repositories at boot

A pull request associated with CVM-872 and CVM-925 disabled mounting of cvmfs repositories at boot by default. Discussion in the pull request said it should be documented to tell system administrators they can add a boot script to mount the repositories themselves. However I don't think there's a convenient method for a system administrator to use. I believe there should be something like a cvmfs_server mount -a option that they can call.

I suppose there might as well be a cvmfs_server umount if there's a cvmfs_server mount.