qmp: Split ShutdownCause host-qmp into quit and system-reset

It is interesting to know whether the shutdown cause was 'quit' or
'reset', especially when using "--no-reboot". In that case, a management
layer can now determine if the guest wanted a reboot or shutdown, and
can act accordingly.

Changes the output of the reason in the iotests from 'host-qmp' to
'host-qmp-quit'. This does not break compatibility because
the field was introduced in the same version.

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
Message-Id: <20181205110131.23049-4-d.csapak@proxmox.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Commit message tweaked]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
diff --git a/tests/qemu-iotests/184.out b/tests/qemu-iotests/184.out
index 0ce9e48..3deb3cf 100644
--- a/tests/qemu-iotests/184.out
+++ b/tests/qemu-iotests/184.out
@@ -95,7 +95,7 @@
     "event": "SHUTDOWN",
     "data": {
         "guest": false,
-        "reason": "host-qmp"
+        "reason": "host-qmp-quit"
     }
 }
 
@@ -175,7 +175,7 @@
     "event": "SHUTDOWN",
     "data": {
         "guest": false,
-        "reason": "host-qmp"
+        "reason": "host-qmp-quit"
     }
 }
 
@@ -217,7 +217,7 @@
     "event": "SHUTDOWN",
     "data": {
         "guest": false,
-        "reason": "host-qmp"
+        "reason": "host-qmp-quit"
     }
 }
 
@@ -253,7 +253,7 @@
     "event": "SHUTDOWN",
     "data": {
         "guest": false,
-        "reason": "host-qmp"
+        "reason": "host-qmp-quit"
     }
 }