LU-16239 tests: do not cleanup clients dirs

LU-16239 tests: do not cleanup clients dirs

Patch adds the ability to not remove the clients
directories. Let's just rename them if CLEANUP set to
false.

Test-Parameters: trivial
Signed-off-by: Elena Gryaznova <elena.gryaznova@hpe.com>
HPE-bug-id: LUS-11158
Reviewed-by: Vladimir Saveliev <vladimir.saveliev@hpe.com>
Reviewed-by: Alexander Boyko <alexander.boyko@hpe.com>
Change-Id: Ibc55d32ef4946a62b00dcbf745567c123650ced9
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/48870
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>