Move dynamic grouping conditional

Instead of using a when clause around the inclusion of the
dynamic-grouping task, use a new var, 'group_when' that's only applied
within the task. This will avoid checking localhost for a hostvar which
doesn't actually apply and may not exist.

Change-Id: I44fa2b0e5b62f632c4b2fe2cc453d08692d97544

playbooks/common-tasks/dynamic-grouping.yml

@@ -13,12 +13,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-- name: Add {{ inventory_hostname }} to dynamic inventory group
+- name: Add hosts to dynamic inventory group
   add_host:
     group: "{{ dest_group }}"
     name: "{{ item }}"
   with_items: "{{ groups[src_group] }}"
   when:
-    - "src_group in groups"
+    - "group_when | default(True)"
   tags:
     - common-grouping

playbooks/os-neutron-install.yml

@@ -23,8 +23,8 @@
       vars:
         src_group: "nova_compute"
         dest_group: "neutron_l3_agent, neutron_metadata_agent"
-      when:
-        - "neutron_plugin_type == 'ml2.ovs.dvr'"
+        group_when:
+          - "neutron_plugin_type == 'ml2.ovs.dvr'"