Do not search osd ids if ceph-volume

Description of problem: The 'get osd id' task goes through all the 10 times (and its respective timeouts) to make sure that the number of OSDs in the osd directory match the number of devices.

This happens always, regardless if the setup and deployment is correct.

Version-Release number of selected component (if applicable): Surely the latest. But any ceph-ansible version that contains ceph-volume support is affected.

How reproducible: 100%

Steps to Reproduce:
1. Use ceph-volume (LVM) to deploy OSDs
2. Avoid using anything in the 'devices' section
3. Deploy the cluster

Actual results:
TASK [ceph-osd : get osd id _uses_shell=True, _raw_params=ls /var/lib/ceph/osd/ | sed 's/.*-//'] **********************************************************************************************************************************************
task path: /Users/alfredo/python/upstream/ceph/src/ceph-volume/ceph_volume/tests/functional/lvm/.tox/xenial-filestore-dmcrypt/tmp/ceph-ansible/roles/ceph-osd/tasks/start_osds.yml:6
FAILED - RETRYING: get osd id (10 retries left).
FAILED - RETRYING: get osd id (9 retries left).
FAILED - RETRYING: get osd id (8 retries left).
FAILED - RETRYING: get osd id (7 retries left).
FAILED - RETRYING: get osd id (6 retries left).
FAILED - RETRYING: get osd id (5 retries left).
FAILED - RETRYING: get osd id (4 retries left).
FAILED - RETRYING: get osd id (3 retries left).
FAILED - RETRYING: get osd id (2 retries left).
FAILED - RETRYING: get osd id (1 retries left).
ok: [osd0] => {
    "attempts": 10,
    "changed": false,
    "cmd": "ls /var/lib/ceph/osd/ | sed 's/.*-//'",
    "delta": "0:00:00.002717",
    "end": "2018-01-21 18:10:31.237933",
    "failed": true,
    "failed_when_result": false,
    "rc": 0,
    "start": "2018-01-21 18:10:31.235216"
}

STDOUT:

0
1
2

Expected results:
There aren't any (or just a few) timeouts while the OSDs are found

Additional info:
This is happening because the check is mapping the number of "devices" defined for ceph-disk (in this case it would be 0) to match the number of OSDs found.

Basically this line:

    until: osd_id.stdout_lines|length == devices|unique|length

Means in this 2 OSD case it is trying to ensure the following incorrect condition:

    until: 2 == 0

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=1537103

roles/ceph-osd/tasks/start_osds.yml

@@ -12,6 +12,8 @@
   register: osd_id
   until: osd_id.stdout_lines|length == devices|unique|length
   retries: 10
+  when:
+    - osd_scenario != 'lvm'
 
 - name: ensure systemd service override directory exists
   file: