Reduce the default number of attempts to start the broker in tests

With the containerized CI environment, port conflicts are much less
likely, so reducing the attempt count improves the feedback loop

deps/rabbitmq_ct_helpers/src/rabbit_ct_broker_helpers.erl

@@ -178,7 +178,7 @@
   ]).
 
 -define(DEFAULT_USER, "guest").
--define(NODE_START_ATTEMPTS, 10).
+-define(NODE_START_ATTEMPTS, 3).
 
 -define(TCP_PORTS_BASE, 21000).
 -define(TCP_PORTS_LIST, [