Added configuration options for custom redis servers as well as bin locations

Gitlab-Shell currently has the path and server for Redis hard-coded within lib/gitlab_update.rb.

With this patch users will be able to modify the redis settings within config.yml to successfully display commit notices on their Dashboards since gitlab will pickup the commit notices from Sidekiq/Redis.

Offending line causing a headache as git commits were not being posted to the user and project dashboard:
```command = "env -i redis-cli rpush 'resque:gitlab:queue:post_receive' '{\"class\":\"PostReceive\",\"args\":[\"#{@repo_path}\",\"#{@oldrev}\",\"#{@newrev}\",\"#{@refname}\",\"#{@key_id}\"]}' > /dev/null 2>&1" ```

I've included the option to control the namespace, because it must be specified in gitlab's resque.yml + environments/*.yml  under cache as **:redis_store, "redis://redis.example.com:port/namespace**

Validated against ruby **v1.9.3-p392** and rspec **v2.12.0**