Heka template missing optional params

If enable_rabbitmq or enable_keystone are false, the configs will not be
copied to target nodes for these. This resulted in Heka failing to
start.

Change-Id: I93d15534802b671f1f42e8b2dfb523a17526ffb7
Closes-Bug: #1630613

ansible/roles/common/templates/heka.json.j2

@@ -61,7 +61,8 @@
             "source": "{{ container_config_directory }}/heka-rabbitmq.toml",
             "dest": "/etc/heka/heka-rabbitmq.toml",
             "owner": "heka",
-            "perm": "0600"
+            "perm": "0600",
+            "optional": {{ (not enable_rabbitmq | bool) | string | lower }}
         },
         {
             "source": "{{ container_config_directory }}/heka-openstack.toml",
@@ -80,7 +81,8 @@
             "source": "{{ container_config_directory }}/heka-keystone.toml",
             "dest": "/etc/heka/heka-keystone.toml",
             "owner": "heka",
-            "perm": "0600"
+            "perm": "0600",
+            "optional": {{ (not enable_keystone | bool) | string | lower }}
         },
         {
             "source": "{{ container_config_directory }}/heka-horizon.toml",