Adds support for PodCIDR allocation from the GCE cloud provider

If CIDRAllocatorType is set to `CloudCIDRAllocator`, then allocation
of CIDR allocation instead is done by the external cloud provider and
the node controller is only responsible for reflecting the allocation
into the node spec.

- Splits off the rangeAllocator from the cidr_allocator.go file.
- Adds cloudCIDRAllocator, which is used when the cloud provider allocates
  the CIDR ranges externally. (GCE support only)
- Updates RBAC permission for node controller to include PATCH

cmd/kube-controller-manager/app/controllermanager.go

@@ -477,6 +477,7 @@ func StartControllers(controllers map[string]InitFunc, s *options.CMServer, root
 			serviceCIDR,
 			int(s.NodeCIDRMaskSize),
 			s.AllocateNodeCIDRs,
+			nodecontroller.CIDRAllocatorType(s.CIDRAllocatorType),
 			s.EnableTaintManager,
 			utilfeature.DefaultFeatureGate.Enabled(features.TaintBasedEvictions),
 		)