LU-14960 tests: enhance ha.sh to work with several test dirs

LU-14960 tests: enhance ha.sh to work with several test dirs

Patch adds the ability to work with several test directories
set via ha_test_dirs variable.
Useful for emulation more Lustre clients.
Example:
  before the test mount Lustre on:
    /mnt/lustre, /mnt/lustre1 /mnt/lustre3
  Run ha.sh with:
  ha_test_dirs="/mnt/lustre /mnt/lustre1 /mnt/lustre3"
  The client's test directories will be created in the listed
  test directories:
  client0 works in /mnt/lustre subdirectory
  client1 works in /mnt/lustre1 subdirectory,
  etc.

Patch also adds the ability to not remove the test directories
if CLEANUP set to false.

Test-Parameters: trivial
Signed-off-by: Elena Gryaznova <elena.gryaznova@hpe.com>
HPE-bug-id: LUS-9705
Reviewed-by: Alexander Boyko <alexander.boyko@hpe.com>
Reviewed-by: Andrew Perepechko <andrew.perepechko@hpe.com>
Change-Id: I1d04b7deeda693c9ca1c86411b0a66c6a2315923
Reviewed-on: https://review.whamcloud.com/44739
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>