rabbit_khepri: Fix force_reset/0 to work with stopped Ra system

[Why]
This function blindly relied on the fact that the Ra `coordination`
system was not stopped by `rabbit` when it stopped. That Ra system is
finally correctly stopped in the parent commit. This breaks this
function and it must be adapted to work with the Ra system stopped.

This is even safer because the function deletes the Ra system directory
as its last step.

[How]
The Ra system data directory is queried from RabbitMQ configuration
instead of the running Ra system.

We add a couple assertions to ensure the conditions are the ones we
expect.

deps/rabbit/src/rabbit_khepri.erl

@@ -509,8 +509,21 @@ reset() ->
 %% @private
 
 force_reset() ->
-    DataDir = maps:get(data_dir, ra_system:fetch(coordination)),
-    ok = rabbit_file:recursive_delete(filelib:wildcard(DataDir ++ "/*")).
+    %% The Ra `coordination' system is stopped at this point; we assert that
+    %% with the `ra_system:fetch/1' call below. Therefore, we take the data
+    %% directory from the configuration.
+    RaSystem = coordination,
+    ?assertEqual(undefined, ra_system:fetch(RaSystem)),
+    Config = rabbit_ra_systems:get_config(RaSystem),
+    DataDir = maps:get(data_dir, Config),
+    ?assert(string:length(DataDir) > 0), %% Assertion to not `rm -rf /'.
+    ?LOG_INFO(
+       "Deleting Ra `coordination` system data directory as part of "
+       "Khepri reset: ~ts",
+       [DataDir],
+       #{domain => ?RMQLOG_DOMAIN_GLOBAL}),
+    Glob = filename:join(DataDir, "*"),
+    ok = rabbit_file:recursive_delete(filelib:wildcard(Glob)).
 
 %% @private
 

deps/rabbit/src/rabbit_ra_systems.erl

@@ -13,6 +13,7 @@
 
 -export([setup/0,
          setup/1,
+         get_config/1,
          all_ra_systems/0,
          are_running/0,
          ensure_ra_system_started/1,