Define condition for the first play host one time

We use the same condition, which defines against what host some "service"
tasks should run against, several times. It's hard to keep it the same
across the role and ansible spending additional resources to evaluate
it each time, so it's simpler and better for the maintenance to set
a boolean variable which will say for all tasks, that we want to run
only against signle host, if they should run or not now.

Change-Id: I4abb67271bd635c8cde5d4d65451e5fa0091868b

tasks/main.yml

@@ -135,8 +135,7 @@
 
 - import_tasks: mq_setup.yml
   when:
-    - "swift_services['swift-proxy-server']['group'] in group_names"
-    - "inventory_hostname == ((groups[swift_services['swift-proxy-server']['group']]| intersect(ansible_play_hosts)) | list)[0]"
+    - _swift_proxy_is_first_play_host
   vars:
     _oslomsg_configure_notify: "{{ swift_ceilometer_enabled | bool }}"
     _oslomsg_notify_setup_host: "{{ swift_oslomsg_notify_setup_host }}"
@@ -184,7 +183,7 @@
   when:
     - "swift_do_setup | bool"
     - '"keystoneauth" in swift_middleware_list'
-    - "inventory_hostname == ((groups['swift_all'] | intersect(ansible_play_hosts)) | list)[0]"
+    - _swift_proxy_is_first_play_host
   tags:
     - swift-config
 

tasks/swift_post_install.yml

@@ -48,4 +48,4 @@
   delegate_to: "{{ item }}"
   with_items: "{{ groups['swift_proxy'] }}"
   when:
-    - "inventory_hostname == ((groups['swift_proxy'] | intersect(ansible_play_hosts)) | list)[0]"
+    - _swift_proxy_is_first_play_host

tasks/swift_rings.yml

@@ -16,14 +16,14 @@
 - include_tasks: swift_rings_md5sum.yml
 
 - include_tasks: swift_rings_check.yml
-  when: inventory_hostname == groups['swift_hosts'][0]
+  when: _swift_is_first_play_host
 
 - include_tasks: swift_rings_build.yml
-  when: inventory_hostname == groups['swift_hosts'][0]
+  when: _swift_is_first_play_host
 
 - include_tasks: swift_rings_distribute.yml
 
 - include_tasks: swift_rings_md5sum.yml
 
 - include_tasks: swift_rings_post_distribution_check.yml
-  when: inventory_hostname == groups['swift_hosts'][0]
+  when: _swift_is_first_play_host

vars/main.yml

@@ -13,6 +13,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+_swift_proxy_is_first_play_host: "{{ (swift_services['swift-proxy-server']['group'] in group_names and inventory_hostname == (groups[swift_services['swift-proxy-server']['group']] | intersect(ansible_play_hosts)) | first) | bool }}"
+_swift_is_first_play_host: "{{ ('swift_hosts' in group_names and inventory_hostname == (groups['swift_hosts'] | intersect(ansible_play_hosts)) | first) | bool }}"
+
 filtered_swift_services: |-
   {% set services = [] %}
   {% for key,value in swift_services.items() %}