qa: Fix traceback during fs cleanup between tests

qa: Fix traceback during fs cleanup between tests

The 'mon_allow_pool_delete' option is set to 'True'
in 'setUp' of 'TestVolumes' and is cleared of in
corresponding 'tearDown' function. Hence, any pool
deletion in parent classes such as 'CephFSTestCase'
would fail. This patch fixes the same by setting
the config 'mon_allow_pool_delete' option in the
'CephFSTestCase'.

Fixes: https://tracker.ceph.com/issues/46597
Signed-off-by: Kotresh HR <khiremat@redhat.com>
(cherry picked from commit 381925d219ac2c847947ae1deeab31d6cc2f668f)