@Override
        protected void rollbackFailed(Throwable cause) {
            logStopFailure(cause);
        }
Closes all channels and terminates all event loops.
<ol>
  <li>Closes all server channels so that we don't accept any more incoming connections.</li>
  <li>Closes all accepted channels.</li>
  <li>Shuts down the worker group if necessary.</li>
  <li>Shuts down the boss groups.</li>
</ol>
Note that we terminate the boss groups lastly so that the JVM does not terminate itself
even if other threads are daemon, because boss group threads are always non-daemon.
core/src/main/java/com/linecorp/armeria/server/Server.java