Bookie server runtime.exit() never trigger after registerBookie failed

**BUG REPORT**
Bookie server runtime.exit() never trigger after registerBookie failed
```
try {
stateManager.registerBookie(true).get();
} catch (Exception e) {
LOG.error("Couldn't register bookie with zookeeper, shutting down : ", e);
shutdown(ExitCode.ZK_REG_FAIL);
}
```
***Describe the bug***

After zookeeper and bookkeeper shutdown ungracefully
bookkeeper startup before zookeeper
then bookkeeper register ephemeral znode failed
bookie server is expected to shutdown, it did.
but jvm is still running, it is expected to exit after bookie server shutdown.

**Log:**
```
Couldn't register bookie with zookeeper, shutting down :
java.util.concurrent.ExecutionException: java.io.IOException: org.apache.bookkeeper.bookie.BookieException$MetadataStoreException: java.io.IOException: ZK exception checking and wait ephemeral znode xxx expired
```

i'am sorry, i can't show more log for some reason. but it is the key log.

***To Reproduce***

1. modify zookeeper config ticktime bigger. such as 200s. easy to reproduce
2. shutdown bookkeeper and zookeeper **ungracefully**
3. make bookkeeper start up before zookeeper
4. bookkeeper can startup failed for other reason, i set it in k8s, crashed bookkeeper will start up again till the described bug come up

***Expected behavior***
throw exception in blow **catch** block will trigger exceptionhandler and shutdown hook then fix this problem
```
try {
stateManager.registerBookie(true).get();
} catch (Exception e) {
LOG.error("Couldn't register bookie with zookeeper, shutting down : ", e);
shutdown(ExitCode.ZK_REG_FAIL);
}
```

but i wonder why **shutdown()** don't close future in the main thread
it seem that exceptionhandler and shutdownhook can only be trigger by unhandled exception then close future

there should be better way to fix.