ceph-config: use 'lvm list' to find num_osds for an existing cluster

This makes finding num_osds idempotent for clusters that were deployed
using 'lvm batch'.

Signed-off-by: Andrew Schoen <aschoen@redhat.com>

roles/ceph-config/tasks/main.yml

@@ -38,6 +38,7 @@
         report: true
         action: "batch"
       register: lvm_batch_report
+      failed_when: false
       environment:
         CEPH_VOLUME_DEBUG: 1
       when:
@@ -50,6 +51,26 @@
       when:
         - devices | default([]) | length > 0
         - osd_scenario == 'lvm'
+        - (lvm_batch_report.stdout | from_json).changed
+
+    - name: run 'ceph-volume lvm list' to see how many osds have already been created
+      ceph_volume:
+        action: "list"
+      register: lvm_list
+      environment:
+        CEPH_VOLUME_DEBUG: 1
+      when:
+        - devices | default([]) | length > 0
+        - osd_scenario == 'lvm'
+        - not (lvm_batch_report.stdout | from_json).changed
+
+    - name: set_fact num_osds from the output of 'ceph-volume lvm list'
+      set_fact:
+        num_osds: "{{ lvm_list.stdout | from_json | length | int }}"
+      when:
+        - devices | default([]) | length > 0
+        - osd_scenario == 'lvm'
+        - not (lvm_batch_report.stdout | from_json).changed
 
     when:
       - inventory_hostname in groups.get(osd_group_name, [])