LU-11492 tests: fix thread_sanity() defect

LU-11492 tests: fix thread_sanity() defect

tmin, tmax, tstarted are not set if do_facet fails by some reason.
This leads to the following failure:
Assertion 28 failed: (($tstarted >= $tmin && $tstarted <= $tmax ))
   (expanded: ((16 >=  && 16 <= 16 )))
Patch sets variables equal to 0 for cases of failed do_facet, like
it is done for other similar cases.

Test-Parameters:trivial testlist=sanity envdefinitions=ONLY="53a 53b"
Signed-off-by: Elena Gryaznova <c17455@cray.com>
Cray-bug-id: LUS-5638
Reviewed-by: Alexander Boyko <c17825@cray.com>
Reviewed-by: Vitaly Fertman <c17818@cray.com>
Change-Id: If713ba20a0f71cb17208f776a9a4edd359c07c43
Reviewed-on: https://review.whamcloud.com/33335
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alexandr Boyko <c17825@cray.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>