LU-15298 tests: set mdt_hash permanently

LU-15298 tests: set mdt_hash permanently

On failover setup where <mdtN>_HOST != <mdtNfailover>_HOST
"do_nodes $(comma_list $(mdts_nodes)) lctl set_param" fails:
  set_param: param_path 'lod/*/mdt_hash': No such file or directory
if mdtN facet is active and up on <mdtNfailover>_HOST.
Let's set this parameter permanently.

Fixes: 0a1cf8da80 ("LU-11025 dne: introduce new directory hash type: "crush"")
Signed-off-by: Elena Gryaznova <elena.gryaznova@hpe.com>
HPE-bug-id: LUS-10601
Reviewed-by: Vladimir Saveliev <vlaidimir.saveliev@hpe.com>
Change-Id: Ie36745cdc5fde4a33387baafe146e06ce8812eb4
Reviewed-on: https://review.whamcloud.com/45693
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alexander Zarochentsev <alexander.zarochentsev@hpe.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>