Remove `varnish` parts not to install it.

This commit refs #69.
Add dependency on `nginx`.

This commit refs #69.
Install `nginx`.

This commit refs #69.
Deploy `nginx` configuration file for sensu.kazu634.com.

This commit refs #69.
Add tests for installing `sensu` client.

This commit refs #69.
Merge pull request #69 from kazu634/id/69

[sensu-custom] varnishではなくnginxを利用する