Add console commands to inspect ensemble system

riak_kv_console:ensemble_status([]) prints an overview of the consensus
system, including an overview of all running ensembles.

riak_kv_console:ensemble_status([Label) prints details about a specific
ensemble, with Label corresponding to the printed label for that ensemble
in the overview output.

Examples of command output in various scenarios can be printed by running
riak_kv_ensemble_console:print_variations().
Update dialyzer.ignore-warnings
Fix 2 ensemble-status problems

Instead of crashing, print friendly messages if:
* Strong consistency is disabled
* An invalid non-number ensemble id is passed
Merge pull request #979 from basho/feature/ensemble-commands

Add console commands to inspect ensemble system

Reviewed-by: engelsanchez