Problem: rpl_gtid_server_sighup.test is failing sporadically with result mismatch.
A rotate event is getting generated in the relay logs sporadically.

Analysis: The test script tests sighup signal (flush logs) behaviour 
on both master and slave i.e., the test runs in two iteration
first iteration on master and second iteration on slave. At the end
of the each iteration, test restarts server to make sure that
newly generated binary log/relay log does not cause any issues.
After the first iteration's restart, we must be sure that the IO
thread has connected again with the master that has just restarted,
or else the results of the test case may vary.

Fix: A sync with slave is added after end of the first iteration.