LU-13445 tests: enhance ha.sh to support different users

LU-13445 tests: enhance ha.sh to support different users

Patch adds the ability to run mpi workloads from different users.
The list of users is configured by parameter ha_mpi_users, default
is "mpiuser". Useful for Quota Pools testing.

Test-Parameters: trivial
Cray-bug-id: LUS-8603
Signed-off-by: Elena Gryaznova <elena.gryaznova@hpe.com>
Reviewed-by: Sergey Cheremencev <c17829@cray.com>
Reviewed-by: Vladimir Saveliev <c17830@cray.com>
Change-Id: I848e5eda4e8221ad0edde62f05d5c367d2156966
Reviewed-on: https://review.whamcloud.com/38201
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Sergey Cheremencev <sergey.cheremencev@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>