RunState: Add additional states

Currently, only vm_start() and vm_stop() change the VM state.
That's, the state is only changed when starting or stopping the VM.

This commit adds the runstate_set() function, which makes it possible
to also do state transitions when the VM is stopped or running.

Additional states are also added and the current state is stored.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>

cpus.c

@@ -124,6 +124,7 @@ static void do_vm_stop(RunState state)
         cpu_disable_ticks();
         vm_running = 0;
         pause_all_vcpus();
+        runstate_set(state);
         vm_state_notify(0, state);
         qemu_aio_flush();
         bdrv_flush_all();