The client support objects have previously not been exposed publicly, and only used in tests, so this has never been an issue before. I don't think we should be exposing this on the entity interface, so I suggest that the `Closeable` interface be added back, but the public `getClient()` method on the entity should be made private.

Instead, places where it is called like [this](https://github.com/sjcorbett/brooklyn/blob/f57b5d610a25caa1439823b3f2276b9aeaf72d5b/software/nosql/src/main/java/brooklyn/entity/nosql/mongodb/MongoDBReplicaSetImpl.java#L208):

    primary.getClient().addMemberToReplicaSet(secondary, nextMemberId.incrementAndGet());
    primary.getClient().removeMemberFromReplicaSet(member);

Should be replaced with calls to specific effectors on the entity interface, like this:

    MongoDBServer#addMemberToReplicaSet(MongoDBServer, int);
    MongoDBServer#removeMemberFromReplicaSet(MongoDBServer);

The `MongoDBClientSupport` class itself would still remain as a field in the server entity which would `close()` it during `stop()` execution. It would also still be used in tests, like other client support objects.