Fix rpl.rpl_rotate_logs to work with --repeat

(It's not using include/rpl_init.inc, so it needs to reset the GTID position
explicitly).
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>

mysql-test/suite/rpl/r/rpl_rotate_logs.result

 connect  master,localhost,root,,test,$MASTER_MYPORT,$MASTER_MYSOCK;
 connect  slave,localhost,root,,test,$SLAVE_MYPORT,$SLAVE_MYSOCK;
+SET GLOBAL gtid_slave_pos= "";
 connection slave;
 CALL mtr.add_suppression("Unsafe statement written to the binary log using statement format since BINLOG_FORMAT = STATEMENT.");
 start slave;

mysql-test/suite/rpl/t/rpl_rotate_logs.test

@@ -20,6 +20,9 @@
 connect (master,localhost,root,,test,$MASTER_MYPORT,$MASTER_MYSOCK);
 connect (slave,localhost,root,,test,$SLAVE_MYPORT,$SLAVE_MYSOCK);
 
+# Reset the GTID position explicitly (since we're not using rpl_init.inc).
+SET GLOBAL gtid_slave_pos= "";
+
 # Create empty file
 let $MYSQLD_SLAVE_DATADIR= `select @@datadir`;
 write_file $MYSQLD_SLAVE_DATADIR/master.info;