Make DB host for MaaS configurable

Change-Id: I54f2113ac1d067a327668dda3aee288b9ad0f407
Related-prod: PROD-28242 (PROD:28242)
diff --git a/defaults/maas.yml b/defaults/maas.yml
index df932c8..795d4b0 100644
--- a/defaults/maas.yml
+++ b/defaults/maas.yml
@@ -1,5 +1,6 @@
 parameters:
   _param:
+    maas_postgresql_server: ${_param:postgresql_server}
     default_local_mirrror_content:
       maas_mirror_image_sections:
         bootloaders:
diff --git a/maas/region/single.yml b/maas/region/single.yml
index 96ba7c6..52a613e 100644
--- a/maas/region/single.yml
+++ b/maas/region/single.yml
@@ -49,7 +49,7 @@
         email:  email@example.com
       database:
         engine: postgresql
-        host: localhost
+        host: ${_param:maas_postgresql_server}
         name: maasdb
         password: ${_param:maas_db_password}
         username: maas