LU-10655 tests: eliminate 'ssh exited with exit code 1'

LU-10655 tests: eliminate 'ssh exited with exit code 1'

Eliminate meaningless 'ssh exited with exit code 1' issued by stop()
and wait_exit_ST()

Signed-off-by: Vladimir Saveliev <c17830@cray.com>
Reviewed-by: Elena V. Gryaznova <c17455@cray.com>
Cray-bug-id: MRP-1483
Change-Id: Ie1af3cda0b48b7bf482ea35b84c93e38d0f6c0a9
Test-Parameters: trivial
Reviewed-on: https://review.whamcloud.com/31263
Reviewed-by: Elena Gryaznova <c17455@cray.com>
Tested-by: Jenkins
Reviewed-by: Sergey Cheremencev <c17829@cray.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>