Adapt to scheduler changes in openwhisk. (#132)

- The scheduler PR apache/openwhisk#4984 introduced
  changes that required adaption in the setup of the openwhisk environment used for the automated tests.

Author: falkzoll

ansible/environments/local/hosts

@@ -22,6 +22,9 @@ invoker0            ansible_host=172.17.0.1 ansible_connection=local
 [db]
 172.17.0.1          ansible_host=172.17.0.1 ansible_connection=local
 
+[elasticsearch:children]
+db
+
 [redis]
 172.17.0.1          ansible_host=172.17.0.1 ansible_connection=local