Don't catch exit:{aborted, _} inside mnesia transactions

This is used by mnesia internally to retry deadlocked transaction,
so we should allow it to propagate.

This could be triggered by calling create_node concurrently from
multiple processes and did lead to {cyclic, ...} errors.

src/mod_pubsub.erl

@@ -3920,6 +3920,8 @@ do_transaction(ServerHost, Fun, Trans, DBType) ->
     F = fun() ->
 		try Fun()
                 catch
+					exit:{aborted, _} = Err when DBType == mnesia ->
+						exit(Err);
                     Class:Reason:StackTrace when (DBType == mnesia andalso
                                                   Trans == transaction) orelse
                                                  DBType == sql ->