LU-9474 tests: fix quoting in stack_trap

LU-9474 tests: fix quoting in stack_trap

stack_trap() mishandled single quotes. This patch is not the cleanest
of fixes, but it works.

(sanity-hsm is the only test suite that uses the function, for now)

Test-Parameters: trivial testlist=sanity-hsm
Signed-off-by: Quentin Bouget <quentin.bouget@cea.fr>
Change-Id: Ia43219e57079abdbfc75485105d572bbfa85caba
Reviewed-on: https://review.whamcloud.com/30490
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: James Nunez <james.a.nunez@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>