Fix isolation level in AWS Aurora

If aurora_read_replica_read_committed is set, isolation level is
internally reset so that it will be set again.
This solves the weird behavior in AWS Aurora related to isolation level
as described in
https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/AuroraMySQL.Reference.html#AuroraMySQL.Reference.IsolationLevels

Basically, to change isolation level you must first set
aurora_read_replica_read_committed , and then isolation level

lib/MySQL_Session.cpp

@@ -2453,8 +2453,17 @@ bool MySQL_Session::handler_again___status_SETTING_GENERIC_VARIABLE(int *_rc, co
 			else {
 				sprintf(query,q,"tx_isolation", var_value);
 			}
-		}
-		else {
+		} else if (strncasecmp("aurora_read_replica_read_committed", var_name, 34) == 0) {
+			MySQL_Connection *beconn = mybe->server_myds->myconn;
+			if (beconn->var_hash[SQL_ISOLATION_LEVEL] != 0) {
+				beconn->var_hash[SQL_ISOLATION_LEVEL] = 0;
+				if (beconn->variables[SQL_ISOLATION_LEVEL].value) {
+					free(beconn->variables[SQL_ISOLATION_LEVEL].value);
+					beconn->variables[SQL_ISOLATION_LEVEL].value = NULL;
+				}
+			}
+			sprintf(query,q,var_name, var_value);
+		} else {
 			sprintf(query,q,var_name, var_value);
 		}
 		query_length=strlen(query);