LVM agents: Handle RAID logical volumes (by volume group).

This commit addresses rhbz824153. Specifically, it enables the use
of RAID logical volumes in HA-LVM when using the "tagging" (i.e.
not "clvm") method. Commit f8a488e3977a3104ac50628e709131b99f0c4bcf
handled only a single logical volume per service (i.e. "by LV"), this
patch finishes the job by handling all the LVs in a particular
volume group per service (i.e. "by VG").