name event_loop_group cleanup thread

this butchered name is the best I could come up with <= 15 chars

source/event_loop.c

@@ -67,6 +67,7 @@ static void s_aws_event_loop_group_shutdown_async(struct aws_event_loop_group *e
 
     struct aws_thread_options thread_options = *aws_default_thread_options();
     thread_options.join_strategy = AWS_TJS_MANAGED;
+    thread_options.name = aws_byte_cursor_from_c_str("EvntLoopCleanup"); /* 15 characters is max for Linux */
 
     aws_thread_launch(&cleanup_thread, s_event_loop_destroy_async_thread_fn, el_group, &thread_options);
 }