Stub shuffle! on the sentinel array for consistent test execution

Ensure that the sentinel array is shuffled in a separate test
Avoid the name clash on #host and #port in #discover_master
Merge pull request #27 from basecrm/consistent_test_execution

Stub shuffle! on the sentinel array for consistent test execution
Merge pull request #28 from basecrm/host_and_port_name_clash_in_discover_master

Avoid the name clash on #host and #port in #discover_master
update redis-sentinel configs
use rspec new syntax
rewrite redis sentinel to follow http://redis.io/topics/sentinel-clients
update README and CHANGELOG
update README