LU-4751 hsm: Fix sanity-hsm tests for non-mrsh $PDSH

LU-4751 hsm: Fix sanity-hsm tests for non-mrsh $PDSH

The workaround for starting backgrounded copytool
monitors via pdsh -Rmrsh is not compatible with non-mrsh
values of $PDSH. This commit adds a branch such that
the workaround is only used when required by the test
cluster environment.

Lustre-commit: 0c261a1fd22a0c867b02baa275ae5023f27d6f5f
Lustre-change: http://review.whamcloud.com/#/c/9587/

Signed-off-by: Michael MacDonald <michael.macdonald@intel.com>
Change-Id: Iab7a94180313170a968c7acbe66919a532f08cfd
Reviewed-on: http://review.whamcloud.com/9593
Tested-by: Jenkins
Reviewed-by: James Nunez <james.a.nunez@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>