Replaced Ketama client with Memcache client

Bumped finagle version to 7.0.0
`client.release()` method was deprecated and in latest version of finagle release method was removed. 7.0 is the earliest version with close method available.

Also `KetamaClientBuilder` was removed from 7.0 hence replacing it with `Memcached.client`. Destination path for both KetamaClient and Memcached client is same, hence the same `nodeString` works.