LU-8691 tests: add mdtest to ha.sh

LU-8691 tests: add mdtest to ha.sh

Patch adds:
- mdtest mpi load;
- ha_simultaneous mode, which allows to reboot
  victim nodes simultaneously.

Test-Parameters: trivial
Seagate-bug-id: MRP-3896
Signed-off-by: Elena Gryaznova <elena.gryaznova@seagate.com>
Reviewed-by: Sergey Cheremencev <sergey.cheremencev@seagate.com>
Reviewed-by: Vladimir Saveliev <vladimir.saveliev@seagate.com>
Change-Id: I2c37f2a383ce2ed475ae14dcfa50a7f7357cb1bf
Reviewed-on: https://review.whamcloud.com/23070
Tested-by: Jenkins
Reviewed-by: Jian Yu <jian.yu@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Nunez <james.a.nunez@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>