Handle error state in waitForVMState

If the virtualization framework returns an error state, vfkit currently
ignores it. This commit catches this error state, and returns an error
when it happens.

cmd/vfkit/main.go

@@ -91,6 +91,9 @@ func waitForVMState(vm *vz.VirtualMachine, state vz.VirtualMachineState) error {
 			if newState == state {
 				return nil
 			}
+			if newState == vz.VirtualMachineStateError {
+				return fmt.Errorf("hypervisor virtualization error")
+			}
 		case <-time.After(5 * time.Second):
 			return fmt.Errorf("timeout waiting for VM state %v", state)
 		}