LU-12470 tests: clear MDT-MDT locks for pdo tests

LU-12470 tests: clear MDT-MDT locks for pdo tests

It is not sufficient to clear client locks to avoid
spillover from one tests to the next in the pdo tests, we
must also clear MDT-MDT locks or we can end up waiting for
one of those.

Lustre-change: https://review.whamcloud.com/35321
Lustre-commit: 43ed7101e10e395839f9406bead6a5ac4fb02997

Test-Parameters: trivial testlist=sanityn
Test-Parameters: fstype=zfs testlist=sanityn
Test-Parameters: mdscount=2 mdtcount=4 testlist=sanityn
Test-Parameters: mdscount=2 mdtcount=4 fstype=zfs testlist=sanityn
Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I8b6a1a6e9a1268a5d87bcb216f54736118ae7ba0
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/35865
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>