Implement cluster CLI commands

Implement the following commands using riak_cli:

* cluster status (improved member-status)
* partition-count
* partitions
* partition id=\<id\>
* partition index=\<index\>
* members

TODO: After merge, some code clean up and boundary checking.

Depends on basho/riak_ee#295
This should change to use `riak_cli_typecast:to_node/1`. Otherwise you end up with the following: 

```
Andrews-MacBook-Pro:riak_ee ajs$ dev/dev1/bin/riak-admin cluster partition-count --node=dev2
+----+----------+-----+
|node|partitions| pct |
+----+----------+-----+
|dev2|    0     |  0.0|
+----+----------+-----+
```