LU-8155 tests: Fix timing of sanity-hsm/16

LU-8155 tests: Fix timing of sanity-hsm/16

sanity-hsm/16 occationally fails due to a timing issue.
The measured duration is 19s when the expected duration
is 20s, this is most likely due to rounding of half seconds.

Test-Parameters: trivial testlist=sanity-hsm

Signed-off-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Change-Id: Iff8b4dec6d9d562b1560cc0101f251bf4b039508
Reviewed-on: http://review.whamcloud.com/20271
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>