add spec about connection of RedisWmrs::SlaveClient
add fuubar for better rspec outputs
add simplecov to measure code coverage
add spec and remove unsed code to increase coverage
add an example about reconnecting the server which failed to connect once
separate before block to define several preconditions
just fix indentation
add examples when failed to connect to sentinnel

and examples when not use sentinel
add an example about RedisWmrs::SlaveClient.ip_and_hostnames
remove code to debug error
remove debug code to clean rspec output with fuubar