test: fixup rbd tests as a side effect of reference counting

test: fixup rbd tests as a side effect of reference counting

Allocate heap objects for Journal, ExclusiveLock and ObjectMap
as these classes are not reference counted. However mock objects
for these classes can be allocated on the stack as ->get() and
->put() operations are no-op.

Signed-off-by: Mahati Chamarthy <mahati.chamarthy@intel.com>
Signed-off-by: Venky Shankar <vshankar@redhat.com>