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/qmp-commands.hx b/qmp-commands.hx
index d1c2c59..d83bce5 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -1573,11 +1573,28 @@
 - "running": true if the VM is running, or false if it is paused (json-bool)
 - "singlestep": true if the VM is in single step mode,
                 false otherwise (json-bool)
+- "status": one of the following values (json-string)
+    "debug" - QEMU is running on a debugger
+    "inmigrate" - guest is paused waiting for an incoming migration
+    "internal-error" - An internal error that prevents further guest
+    execution has occurred
+    "io-error" - the last IOP has failed and the device is configured
+    to pause on I/O errors
+    "paused" - guest has been paused via the 'stop' command
+    "postmigrate" - guest is paused following a successful 'migrate'
+    "prelaunch" - QEMU was started with -S and guest has not started
+    "finish-migrate" - guest is paused to finish the migration process
+    "restore-vm" - guest is paused to restore VM state
+    "running" - guest is actively running
+    "save-vm" - guest is paused to save the VM state
+    "shutdown" - guest is shut down (and -no-shutdown is in use)
+    "watchdog" - the watchdog action is configured to pause and
+     has been triggered
 
 Example:
 
 -> { "execute": "query-status" }
-<- { "return": { "running": true, "singlestep": false } }
+<- { "return": { "running": true, "singlestep": false, "status": "running" } }
 
 EQMP