Unify redis client and handle redis errors

[rahulreddy]

UtapiClient currently does not listen to the redis error event, which may flood the logs when Redis
server is unavailable.
This also calls for unification of the redis client as we want the configuration to be setup in one place for easier maintenance.
Lastly, we want to remove the offline queue option, since there is no limit on the callback queue, it may grow to infinity resulting in a RangeError. This option can be re-introduced later after this PR on ioredis is merged, which gives the developer an option to manage the offline queue
redis/ioredis#241