Neutron L3 service cleanups for hiera json hook

This patch resolves a few issues I noticed when porting our
Neutron L3 service to support the new heat hiera agent hook (which
uses Json instead of Yaml).

 - If NeutronExternalNetworkBridge is an emptry string '' Json was
   dropping the single quotes thus causing the bridge to get set
   incorrectly in the config file. To correct this we use a heat
   conditional to avoid setting the external bridge (the '' default
   is what we want in this case) if the bridge is an empty string.

Change-Id: I5037cbde6b76a37a4c22c4616278420e9d759109
Partial-bug: #1596373

puppet/services/neutron-l3.yaml

@@ -1,4 +1,4 @@
-heat_template_version: 2016-04-08
+heat_template_version: 2016-10-14
 
 description: >
   OpenStack Neutron L3 agent configured with Puppet
@@ -43,6 +43,10 @@ parameters:
       tag: openstack.neutron.agent.l3
       path: /var/log/neutron/l3-agent.log
 
+conditions:
+
+  external_network_bridge_empty: {equals : [{get_param: NeutronExternalNetworkBridge}, "''"]}
+
 resources:
 
   NeutronBase:
@@ -63,12 +67,16 @@ outputs:
         - neutron
       config_settings:
         map_merge:
-          - get_attr: [NeutronBase, role_data, config_settings]
+        - get_attr: [NeutronBase, role_data, config_settings]
+        - neutron::agents::l3::router_delete_namespaces: True
+          neutron::agents::l3::agent_mode: {get_param: NeutronL3AgentMode}
+          tripleo.neutron_l3.firewall_rules:
+            '106 neutron_l3 vrrp':
+              proto: vrrp
+        - 
+          if:
+          - external_network_bridge_empty
+          - {}
           - neutron::agents::l3::external_network_bridge: {get_param: NeutronExternalNetworkBridge}
-            neutron::agents::l3::router_delete_namespaces: True
-            neutron::agents::l3::agent_mode : {get_param: NeutronL3AgentMode}
-            tripleo.neutron_l3.firewall_rules:
-              '106 neutron_l3 vrrp':
-                proto: vrrp
       step_config: |
         include tripleo::profile::base::neutron::l3