peer_discovery_classic_config_SUITE: Increase timetrap for successful_discovery_with_a_subset_of_nodes_coming_online

[Why]
Now that feature flags compatibility is tested first, before
Mnesia-specific checks, when a peer is not started yet, the feature
flags check lasts the entire timeout, so one minute. This retry
mechanism was added to feature flags in #8411.

Thus, instead of 20 seconds, the testcase takes 10 minutes now (10
retries of one minute each).

Author: dumbbell

deps/rabbit/BUILD.bazel

@@ -553,7 +553,7 @@ rabbitmq_suite(
 
 rabbitmq_integration_suite(
     name = "peer_discovery_classic_config_SUITE",
-    size = "medium",
+    size = "large",
     flaky = True,
 )
 

deps/rabbit/test/peer_discovery_classic_config_SUITE.erl

@@ -147,6 +147,9 @@ successful_discovery(Config) ->
                     cluster_members_online(Config, 1)},
                    ?TIMEOUT).
 
+successful_discovery_with_a_subset_of_nodes_coming_online() ->
+    [{timetrap, {minutes, 15}}].
+
 successful_discovery_with_a_subset_of_nodes_coming_online(Config) ->
   ?awaitMatch(
      {M1, M2} when length(M1) =:= 2; length(M2) =:= 2,