MDEV-7430: rpl.rpl_gtid_crash still fails in buildbot

The problem was a too low timeout for slave reconnect. It was set to 9 seconds
(10 retries with 1 second in-between). This is occasinally too short on some
Buildbot hosts, when the test crashes and restarts the master while the slave
IO thread is running.

Fix by increasing --master-retry-count for this test.

mysql-test/suite/rpl/t/rpl_gtid_crash-slave.opt

+--master-retry-count=100