LU-13585 tests: add mustfail check

LU-13585 tests: add mustfail check

Patch adds the possibility to ignore the mpi loads failures
for  particular instances.

This is useful for Quota Pools stress tests which are supposed
to randomly hit QP limits.
The subsets of expected failures is set by specifying NINSTMUSTFAIL.
      0 - mpi tests from all clients must pass (default)
      1 - mpi tests from all clients must fail
      N - mpi tests from one client of Ns must fail.
Set NINSTMUSTFAIL=2 to expect each 2nd mpi instance fail and
NINSTMUSTFAIL=3 to expect each 3d mpi instance fail.

For QP test: the different limits set for users per pool: a half
of users have a small limit which makes IOR to fail:
  small limit is set for user1, user3, user5
  large limit is set for user2, user4
Run N ior instances on N clients, each client/instance uses own
user{1..N}. The test considered as pass-ed if IOR instances failed
on client1, client3, client5.

Test-Parameters: trivial
Signed-off-by: Elena Gryaznova <elena.gryaznova@hpe.com>
HPE-bug-id: LUS-8844, LUS-8504, LUS-8602
Reviewed-by: Vladimir Saveliev <vladimir.saveliev@hpe.com>
Reviewed-by: Sergey Cheremencev <c17829@cray.com>
Change-Id: Ia7c4e394c3724190d6cff9f086f8837e54f6110d
Reviewed-on: https://review.whamcloud.com/38662
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Sergey Cheremencev <sergey.cheremencev@hpe.com>
Reviewed-by: Vladimir Saveliev <c17830@cray.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>