error: New convenience function error_report_err()

I've typed error_report("%s", error_get_pretty(ERR)) too many times
already, and I've fixed too many instances of qerror_report_err(ERR)
to error_report("%s", error_get_pretty(ERR)) as well.  Capture the
pattern in a convenience function.

Since it's almost invariably followed by error_free(), stuff that into
the convenience function as well.

The next patch will put it to use.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

util/error.c

@@ -152,6 +152,12 @@ const char *error_get_pretty(Error *err)
     return err->msg;
 }
 
+void error_report_err(Error *err)
+{
+    error_report("%s", error_get_pretty(err));
+    error_free(err);
+}
+
 void error_free(Error *err)
 {
     if (err) {