Add a delay before the cell discovery

We're seeing a race condition during the upgrade test
for the role which causes the test to fail due to the
compute host not being proerly registered somehow. This
patch introduces a little bit of extra time between the
compute host being available and the cell discovery
executing which seems to help.

The extra delay is *only* executed in the role test
where the nova_discover_hosts_in_cells_interval is set
to -1. In a normal production environment it has no
effect.

Change-Id: Ice9deb82f052075f3b8a6ed1bc2387aac365d1fd

handlers/main.yml

@@ -75,6 +75,14 @@
     - "nova_discover_hosts_in_cells_interval | int < 1"
   listen: "Restart nova services"
 
+- name: Once nova-compute has initialised, wait for it to complete registering
+  pause:
+    minutes: 1
+  when:
+    - "'nova_compute' in group_names"
+    - "nova_discover_hosts_in_cells_interval | int < 1"
+  listen: "Restart nova services"
+
 - name: Reload Nginx
   service:
     name: nginx