FixRegression: fix configuring constraints

 *  Configuring subnets should be possible without explicitly configuring
    fabrics.
 *  Configuring devices should be possible without explicitly configuring
    subnets
 *  Port from: https://gerrit.opnfv.org/gerrit/#/c/47679/

Change-Id: Ib5504d090cc98791224934aa384d7b2ebcf043d5
diff --git a/maas/region.sls b/maas/region.sls
index 90d6657..554f9ba 100644
--- a/maas/region.sls
+++ b/maas/region.sls
@@ -159,7 +159,9 @@
   - name: maas.process_subnets
   - require:
     - module: maas_config
+    {%- if region.get('fabrics', False)  %}
     - module: maas_fabrics
+    {%- endif %}
 {%- endif %}
 
 {%- if region.get('devices', False)  %}
@@ -168,7 +170,9 @@
   - name: maas.process_devices
   - require:
     - module: maas_config
+    {%- if region.get('subnets', False)  %}
     - module: maas_subnets
+    {%- endif %}
 {%- endif %}
 
 {%- if region.get('dhcp_snippets', False)  %}