LU-13584 tests: gather_logs() fix

LU-13584 tests: gather_logs() fix

Fix gather_logs() to work on real HW where server nodes
do not have the access to clients.

Signed-off-by: Elena Gryaznova <elena.gryaznova@hpe.com>
HPE-bug-id: LUS-8888
Reviewed-by: Alexander Lezhoev <alexander.lezhoev@hpe.com>
Reviewed-by: Vladimir Saveliev <vladimir.saveliev@hpe.com>
Change-Id: Ifeea54e20d3123ee64582e32b92a4573e60ff33e
Reviewed-on: https://review.whamcloud.com/38660
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Vladimir Saveliev <c17830@cray.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>