Filter computes with nova_host defined

When adding hosts to aggregates/availability zones, use the nodes
that have nova_host defined. This would exclude blacklisted nodes.

Change-Id: I85599dbb985a9d45e2e7587170c39aa2940ca939
(cherry picked from commit 00a2223)

deployment/nova/nova-az-config.yaml

@@ -82,7 +82,7 @@ outputs:
           os_nova_host_aggregate:
             name: {get_attr: [NovaComputeAvailabilityZoneValue, value]}
             availability_zone: {get_attr: [NovaComputeAvailabilityZoneValue, value]}
-            hosts: "{{ groups['nova_compute'] | default([]) | map('extract', hostvars, 'nova_host') | list }}"
+            hosts: "{{ groups['nova_compute'] | default([]) | map('extract', hostvars, 'nova_host') | select('defined') | list }}"
             auth:
               username: admin
               password: {get_param: AdminPassword}