api: Update folder.PlaceVMsXCluster to support several placement types

The PlaceVmsXCluster API is being updated to provide placement
recommendations for several new "op-types", relocate and reconfigure, in
addition to the original "createAndPowerOn" behavior.  To support the
new capability, the PlaceVmsXCluster API is updated to add a new placement
type field, add 2 new supported placement types (relocate and reconfigure)
and to extend the spec and faults to carry addition info referencing
existing VMs and an optional relocate spec.

This change does the following:
- extends the API definitions to reflect the changes.
- extends the simulator to support these new placement types.
- adds simulator tests to validate the new placement types.

simulator/cluster_compute_resource_test.go

@@ -259,7 +259,7 @@ func TestPlaceVmRelocate(t *testing.T) {
 				"InvalidArgument",
 			},
 			{
-				"relocate with a diskId in spec.dick that does not exist in the vm",
+				"relocate with a diskId in spec.disk that does not exist in the vm",
 				&types.VirtualMachineRelocateSpec{
 					Host: &hostMoRef,
 					Disk: []types.VirtualMachineRelocateSpecDiskLocator{