rolling_update: fix get fsid for containers

rolling_update: fix get fsid for containers

When running ansible2.4-update_docker_cluster there is an issue on the
"get current fsid" task. The current task only works for
non-containerized deployment but will run all the time (even for
containerized). This currently results in the following error:

TASK [get current fsid] ********************************************************
task path: /home/jenkins-build/build/workspace/ceph-ansible-prs-luminous-ansible2.4-update_docker_cluster/rolling_update.yml:214
Tuesday 22 May 2018  22:48:32 +0000 (0:00:02.615)       0:11:01.035 ***********
fatal: [mgr0 -> mon0]: FAILED! => {
    "changed": true,
    "cmd": [
        "ceph",
        "--cluster",
        "test",
        "fsid"
    ],
    "delta": "0:05:00.260674",
    "end": "2018-05-22 22:53:34.555743",
    "rc": 1,
    "start": "2018-05-22 22:48:34.295069"
}

STDERR:

2018-05-22 22:48:34.495651 7f89482c6700  0 -- 192.168.17.10:0/1022712 >> 192.168.17.12:6789/0 pipe(0x7f8944067010 sd=4 :42654 s=1 pgs=0 cs=0 l=1 c=0x7f894405d510).connect protocol feature mismatch, my 83ffffffffffff < peer 481dff8eea4fffb missing 400000000000000
2018-05-22 22:48:34.495684 7f89482c6700  0 -- 192.168.17.10:0/1022712 >> 192.168.17.12:6789/0 pipe(0x7f8944067010 sd=4 :42654 s=1 pgs=0 cs=0 l=1 c=0x7f894405d510).fault

This is not really representative on the real error since the 'ceph' cli is available on that machine.
On other environments we will have something like "command not found: ceph".

Signed-off-by: Sébastien Han <seb@redhat.com>