Improve error message when no viable server is found due to GTID waiting

lib/MySQL_HostGroups_Manager.cpp

@@ -2901,9 +2901,13 @@ MySrvC *MyHGC::get_random_MySrvC(char * gtid_uuid, uint64_t gtid_trxid, int max_
 			}
 			if (t - last_hg_log > 1) { // log this at most once per second to avoid spamming the logs
 				last_hg_log = time(NULL);
-				proxy_error("Hostgroup %u has no servers available%s! Checking servers shunned for more than %u second%s\n", hid,
-				(max_connections_reached ? " or max_connections reached for all servers" : ""),
-				max_wait_sec, max_wait_sec == 1 ? "" : "s");
+
+				if (gtid_trxid) {
+					proxy_error("Hostgroup %u has no servers ready for GTID '%s:%d'. Waiting for replication...\n", hid, gtid_uuid, gtid_trxid);
+				} else {
+					proxy_error("Hostgroup %u has no servers available%s! Checking servers shunned for more than %u second%s\n", hid,
+						(max_connections_reached ? " or max_connections reached for all servers" : ""), max_wait_sec, max_wait_sec == 1 ? "" : "s");
+				}
 			}
 			for (j=0; j<l; j++) {
 				mysrvc=mysrvs->idx(j);