Clean up internal Bookkeeper constructors

[ivankelly]

JIRA: https://issues.apache.org/jira/browse/BOOKKEEPER-1011

Reporter: Robert Joseph Evans @revans2

One of the feedbacks from

#105 (comment)

was that there are some customer APIs that need to be cleaned up. This is specifically for the two constructors in Bookkeeper

{code}
public BookKeeper(ClientConfiguration conf, ZooKeeper zk);
public BookKeeper(ClientConfiguration conf, ZooKeeper zk, ClientSocketChannelFactory channelFactory);
{code}

That are really for internal use only. We should find a way to mark them as such.

[ivankelly]

This should be done as part of new api work. Ideally there should be no constructor for the BookKeeper object, but everything should go through a Builder that returns a o.a.b.client.api.BookKeeper object.

Currently it's not really useful to have o.a.b.client.api.BookKeeper as you have to import o.a.b.client.BookKeeper to create one.

ClientConfiguration should probably be deprecated too, and all the configuration in it put in the builder.

(cc @sijie @eolivelli )

[eolivelli]

We could deprecate current constructors in 4.8.
Once we are OK with new API