Fix net check return error when net_obj get value is "None"
Fix net check return error when net_obj get value is "None"

Closes-Bug: #1777774

Change-Id: I6073a075837ee3fdaa6f09c49b76aacbc0d90226

openstack/senlin,stackforge/senlin,stackforge/senlin,openstack/senlin,openstack/senlin