CLOUDSTACK-4315: VPC - when fail to add nic to the VR, a) remove the nic b) remove the reference to nic from router_network_ref table. Before the fix b) was missing, and it caused NPEs when tried to apply the rules on the routers not having nic in the network

Conflicts:
	server/src/com/cloud/network/element/VirtualRouterElement.java
	server/src/com/cloud/vm/VirtualMachineManagerImpl.java