LU-13279 tests: sanityn.sh:test_20 takes DoM into account

LU-13279 tests: sanityn.sh:test_20 takes DoM into account

sanityn.sh:test_20() should also cancel MDC locks as layout of files
may include DoM component.

Test-Parameters: testlist=sanityn
Cray-bug-id: LUS-8348
Signed-off-by: Vladimir Saveliev <c17830@cray.com>
Change-Id: I6157038235590d3c5b06d910c3b3d2600968a812
Reviewed-on: https://review.whamcloud.com/37662
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Mike Pershin <mpershin@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>