[client] new API to check if Bookkeeper client is connected to metadata service

[congbobo184]

Motivation

when zookeeper disconnect, use bookkeeper api to create new ledger will fail. add a new api to check metadata driver is available, if not available, use current ledger continue and don't rollover ledger

** tip **

Although it may not solve all issues since it's not atomic, it will reduce the losses caused by zk unavailability.

Modification

add a new api named isDriverMetadataServiceAvailable

[congbobo184]

rerun failure checks

[congbobo184]

@shoothzj @eolivelli please review again, thanks

[hezhangjian]

Thanks for your contribution. :)