LU-4249 lquota: Add diagnostic LBUG on lqe_getref/putref

Extra debugging to try to find bad usage of lquota_entry.

Test-Parameters: envdefinitions=SLOW=yes testlist=sanity-quota
Signed-off-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Change-Id: I865294d56584d181c428f2130e627d511dcbc793