报错：
com.cloud.exception.ResourceUnavailableException: Resource [DataCenter:1] is unreachable: Unable to apply dhcp entry on router
at com.cloud.network.router.VirtualNetworkApplianceManagerImpl.applyDhcpEntry(VirtualNetworkApplianceManagerImpl.java:3209)
at com.sun.proxy.$Proxy191.applyDhcpEntry(Unknown Source)
at com.cloud.network.element.VirtualRouterElement.addDhcpEntry(VirtualRouterElement.java:921)
删除vr,再创建新虚拟机就可以了
用一个例子来演示会更加清晰
