Fix the bug of #41

Now, we are able to set any directories to WP_HOME and WP_SITEURL in the Vagrantfile as follows:

`WP_HOME = "/sub"`
`WP_SITEURL = "/sub"`

or

`WP_HOME = "/sub"`
`WP_SITEURL = "/sub/wp"`

or

`WP_HOME = "/sub"`
`WP_SITEURL = "/wp"`

or deeper if you want.