QMP: QError: New QERR_UNSUPPORTED

New QERR_UNSUPPORTED for unsupported commands or requests.

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

qerror.c

diff --git a/qerror.c b/qerror.c
index 4855604..4f3b7ca 100644
--- a/qerror.c
+++ b/qerror.c
@@ -201,6 +201,10 @@
         .desc      = "An undefined error has ocurred",
     },
     {
+        .error_fmt = QERR_UNSUPPORTED,
+        .desc      = "this feature or command is not currently supported",
+    },
+    {
         .error_fmt = QERR_UNKNOWN_BLOCK_FORMAT_FEATURE,
         .desc      = "'%(device)' uses a %(format) feature which is not "
                      "supported by this qemu version: %(feature)",