Change the `Unicorn` configuration, depending on `RACK_ENV` environment variable.

- the path to the application
- listen directive: Unix socket or port number
- pid location directory
- location of the log files, under production environment

This commit refs #2.
Merge pull request #2 from kazu634/id/2

unicornのsocketファイル・pidファイルを/var/runに格納する