First go at cluster status
Export partitions/2 to reuse elsewhere
Continue implementation of cluster commands
Fixes from manual testing
Remove erroneous shortname handlers
Use riak_cli behaviour; use riak_cli_status

Remove all usage of direct io:format in favor of the
riak_cli status types.  This will hopefully simplify
output.
Add cluster_cli to cli registry
Remove dangling list syntax; always return status

After basho/riak_cli#14 was merged, callbacks are expected
to implement riak_cli_status types as their return values.
Remove unnecessary alert() status responses.
Add make_alert/1; cosmetic cleanups.
Merge pull request #659 from basho/feature/mra/cluster-cli

Implement cluster CLI commands

Reviewed-by: andrewjstone