AMBARI-4308. Add optional parameter options and minor fixes to custom action support

ambari-agent/src/main/python/ambari_agent/AmbariConfig.py

@@ -45,7 +45,7 @@ facter_home=/root/workspace/puppet-install/facter-1.6.10
 timeout_seconds = 600
 
 [python]
-custom_actions_dir = /var/lib/ambari-agent/resources
+custom_actions_dir = /var/lib/ambari-agent/resources/custom_actions
 
 [command]
 maxretries=2