LU-14271 tests: add new node crash method

LU-14271 tests: add new node crash method

Patch adds a new node crash method: node crash
is simulated by command executed on the victim nodes.
Example:
  POWER_DOWN=sysrqcrash
triggers a crash  on all victim nodes.

Test-Parameters: trivial
Signed-off-by: Elena Gryaznova <elena.gryaznova@hpe.com>
HPE-bug-id: LUS-8162
Reviewed-by: Vladimir Saveliev <vladimir.saveliev@hpe.com>
Reviewed-by: Sergey Cheremencev <sergey.cheremencev@hpe.com>
Tested-by: Vitaly Fertman <vitaly.fertman@hpe.com>
Change-Id: Id39b0f58fbb59236b3af51516fe968c888b04a17
Reviewed-on: https://review.whamcloud.com/41071
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>