multipath.getMPDevNamesIter() return /dev/mapper.

multipath names return the /dev/mapper part of the path for
consistency with lvm module.

Change-Id: I1ec54147205992ac130684d01e73cd7aceccad48
Signed-off-by: Eduardo <ewarszaw@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/17967
Reviewed-by: Dan Kenigsberg <danken@redhat.com>