Better Handling for enable_consensus [JIRA: TOOLS-255]

[pogzie]

As commented by Kaz in ticket 13306

"Riaknostic verifies the combination of AAE and strong consistency, and expects enable_consensus is always defined as true or false in riak_core section of app.config. If a user uses riak.conf, enable_consensus is generated by cuttlefish. However, a user used app.config which didn't contain enable_consensus config."

A workaround is to use riak.conf, or add the following in riak_core section of app.config:
{enable_consensus, false}