LU-8550 test: fix problems of conf-sanity test_32

LU-8550 test: fix problems of conf-sanity test_32

1) test_32a: The MGS should be umounted otherwise the seperate
MGS will cause failure of conf-sanity 32a. and re-start mgs in
t32_test_cleanup() because mgs need be always started.
2) test_32c: Format and tunefs on the same mds in conf-sanity 32
tests If mds1 and mds2 are different machine, conf-sanity 32c
will fail.

    Test-Parameters: trivial combinedmdsmgs=false envdefinitions=ONLY=32 testlist=conf-sanity

    Test-Parameters: trivial envdefinitions=ONLY=32 testlist=conf-sanity

Change-Id: I16e259d16912f894341a17855aca1e3fbbe6a8f3
Signed-off-by: Gu Zheng <gzheng@ddn.com>
Reviewed-on: https://review.whamcloud.com/22146
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Wang Shilong <wshilong@ddn.com>
Reviewed-by: James Nunez <james.a.nunez@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>