[WIP][kazu634] Supports `kitchen-docker` testing environment.
[kazu634] Supports `kitchen-docker` testing environment.
[kazu634] Remove unnecessary tests.

Because `Ruby` installation process is tested by `rbenv` repository,
remove the unnecessary tests relating to `ruby`.
Merge pull request #153 from kazu634/kazu634-supports-kitchen-docker

[kazu634] Supports `kitchen-docker` testing environment.