error, qerror: pass desc string to error calls

This commit changes all QERR_ macros to contain a human message (ie.
the desc string found in qerr_table[]) instead of a json dictionary
in string format.

Before this commit, error_set() and qerror_report() would receive
a json dictionary in string format and build a qobject from it. Now,
both function receive a human message instead and the qobject is
not built anymore.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
diff --git a/error.c b/error.c
index 9d7b35f..0e10373 100644
--- a/error.c
+++ b/error.c
@@ -37,9 +37,8 @@
     err = g_malloc0(sizeof(*err));
 
     va_start(ap, fmt);
-    err->obj = qobject_to_qdict(qobject_from_jsonv(fmt, &ap));
+    err->msg = g_strdup_vprintf(fmt, ap);
     va_end(ap);
-    err->msg = qerror_format(fmt, err->obj);
     err->err_class = err_class;
 
     *errp = err;