QMP: query-status: Introduce 'status' key

This new key reports the current VM status to clients. Please, check
the documentation being added in this commit for more details.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
diff --git a/monitor.c b/monitor.c
index ac68edf..ab71d2d 100644
--- a/monitor.c
+++ b/monitor.c
@@ -2636,8 +2636,7 @@
 
 static void do_info_status(Monitor *mon, QObject **ret_data)
 {
-    *ret_data = qobject_from_jsonf("{ 'running': %i, 'singlestep': %i }",
-                                    runstate_is_running(), singlestep);
+    *ret_data = qobject_from_jsonf("{ 'running': %i, 'singlestep': %i, 'status': %s }", runstate_is_running(), singlestep, runstate_as_string());
 }
 
 static qemu_acl *find_acl(Monitor *mon, const char *name)