Added support to '!include' mechanism
Added support to '!include' mechanism

The '!include' idiom is used to include an external YAML file into
current one. Currently, it supports protocol like 'file', 'http' and
'https'(not tested).

tengqm/senlin-container,stackforge/senlin,stackforge/senlin,Alzon/senlin,tengqm/senlin,openstack/senlin,Alzon/senlin,tengqm/senlin,tengqm/senlin-container,openstack/senlin,openstack/senlin