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'.