Merge values for same key from multiple services

This should merge multiple and different values for the same key
found in different services.

For example, assuming two services defining a key as follows:

  config_settings:
    mykey:
    - val1

  config_settings:
    mykey:
    - val2
    - val3

the content of the key, as seen by ansible or puppet on the nodes,
will be:

  mykey: ['val1','val2','val3']

Change-Id: I190374e36ad1a2b57611a3a9d0a52ceb1a049aff

common/services.yaml

@@ -365,7 +365,10 @@ outputs:
       monitoring_subscriptions: {get_attr: [MonitoringSubscriptionsConfig, value]}
       logging_sources: {get_attr: [LoggingSourcesConfig, value]}
       logging_groups: {get_attr: [LoggingGroupsConfig, value]}
-      config_settings: {map_merge: {get_attr: [ServiceChain, role_data, config_settings]}}
+      config_settings:
+        yaql:
+          expression: $.data.where($ != null).reduce($1.mergeWith($2), {})
+          data: {get_attr: [ServiceChain, role_data, config_settings]}
       global_config_settings: {get_attr: [GlobalConfigSettings, value]}
       service_config_settings: {get_attr: [ServiceConfigSettings, value]}
       workflow_tasks: {get_attr: [WorkflowTasks, value]}