tests/rgw: add timeout 5s to radosgw-admin command

tests/rgw: add timeout 5s to radosgw-admin command

If the radosgw daemons aren't up and running correctly (like not registered
in the servicemap or the OSD are down) then the radosgw-admin will hang
forever.
Jenkins will kill the jobs after 3h but we don't want to wait until this global
timeout.
Adding the timeout 5 command to the radosgw-admin commands (which is already
present on other ceph calls) allows the job to fail earlier.

Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>