Support different context path

#50, fix the build-screen goes 404 when access ex:) `http://master.pool.dev/path/to/something` includes context path.

I also add test for `hooks.rb` with using infraspec, and serverspec. 🉐
@mookjp Sorry, actually this file is generated automatically by `serverspec-init` command to initialize serverspec test. But `TARGET_HOST` variable may be for referring the hostname variable while executing test to target inside `*_spec.rb` file.