LU-6203 tests: early lock cancel to allow early copytool death

LU-6203 tests: early lock cancel to allow early copytool death

Since copytool death check+timing has been introduced with patch for
LU-5622, sanity-hsm/test_251() has experienced several failures
due to copytool death being delayed and to timeout, because of lock
cancel.

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: I399b37854b98626c4c92a367d543b79aebf9eb4e
Reviewed-on: http://review.whamcloud.com/13646
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Henri Doreau <henri.doreau@cea.fr>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>