Flatten yaql list expressions

In python yaql 2, the expressions are returning a nested list but we
need a list of dictionaries in order to use map_merge.  This change adds
flatten so it returns [] instead of [[]] when nothing is available.

Change-Id: Iba0262fbc2af0903f02c8c28c7ba2b1d935abe7f

deployment/nova/nova-compute-container-puppet.yaml

@@ -1178,7 +1178,7 @@ outputs:
                   - if:
                     - nova_glance_rbd_download_multistore_id_set
                     - yaql:
-                        expression: let(k => $.data.key) -> list(coalesce($.data.multistore, {}).get($k)).select($.get("CephClusterName"))
+                        expression: let(k => $.data.key) -> list(coalesce($.data.multistore, {}).get($k)).flatten().select($.get("CephClusterName"))
                         data:
                           key: {get_attr: [RoleParametersValue, value, nova_glance_rbd_download_multistore_id]}
                           multistore: {get_param: GlanceMultistoreConfig}

extraconfig/nova_metadata/krb-service-principals/role.role.j2.yaml

@@ -55,7 +55,7 @@ resources:
           # 'metadata_settings', get the values from that key and get the
           # unique ones. Also, filter values for networks not associated with
           # this role.
-          expression: let(role_networks => $.data.role_networks) -> list(coalesce($.data.role_data, []).where($ != null).where($.containsKey('metadata_settings')).metadata_settings.flatten().distinct().where($ != null and $.containsKey('network')).where($role_networks.contains($.network)))
+          expression: let(role_networks => $.data.role_networks) -> list(coalesce($.data.role_data, []).where($ != null).where($.containsKey('metadata_settings')).metadata_settings.flatten().distinct().where($ != null and $.containsKey('network')).where($role_networks.contains($.network))).flatten()
           data:
             role_data: {get_param: RoleData}
             role_networks: