cephfs/admin: Rename fs quiesce test file

We do have a test file named fs_quiesce_reef_test.go to make sure
that the feature is supported only from upcoming squid release. The
'reef' keyword doesn't make sense as the test itself is applicable
for any version prior to squid(upcoming). Therefore use a generic
'unsupported' keyword in the test file name.

Signed-off-by: Anoop C S <anoopcs@cryptolab.net>