Added ability to skip enabled backends pre-check

When using custom storage backends with cinder.conf overrides file,
precheck stage in kolla-ansible is fail. This commit adds option
'skip_cinder_backend_check' (default: False) to cinder role.

Change-Id: Ifee138ad8b281903ea2365441aada044c80c46f0

ansible/roles/cinder/defaults/main.yml

@@ -189,6 +189,8 @@ cinder_backends:
   - name: "zfssa-iscsi"
     enabled: "{{ enable_cinder_backend_zfssa_iscsi | bool }}"
 
+skip_cinder_backend_check: False
+
 cinder_enabled_backends: "{{ cinder_backends|selectattr('enabled', 'equalto', true)|list }}"
 
 #############################################

ansible/roles/cinder/tasks/precheck.yml

@@ -20,6 +20,7 @@
   run_once: True
   local_action: fail msg="Please enable at least one backend when enabling Cinder"
   when:
+    - not skip_cinder_backend_check | bool
     - not enable_cinder_backend_hnas_iscsi | bool
     - not enable_cinder_backend_hnas_nfs | bool
     - not enable_cinder_backend_iscsi | bool

doc/source/reference/storage/cinder-guide.rst

@@ -188,3 +188,16 @@ the following parameter must be specified in ``globals.yml``:
    enable_cinder_backend_iscsi: "yes"
 
 Also ``enable_cinder_backend_lvm`` should be set to ``no`` in this case.
+
+Skip Cinder prechecks for Custom backends
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In order to use custom storage backends which currently not yet implemented
+in Kolla, the following parameter must be specified in ``globals.yml``:
+
+.. code-block:: yaml
+
+   skip_cinder_backend_check: True
+
+All configuration for custom NFS backend should be performed
+via ``cinder.conf`` in config overrides directory.