Add support for setting maintenance mode

* If the resource specifies a maintenance page, turn on check for maintenance mode
* Maintenance mode is specified by the presence of a file.
* Maintaince mode file can be specified or defaults to in_maintenance_mode in the parent directory of the root directory
Set default attributes for nginx_passenger

* maintenance_page
* maintenance_check

Also changed the default maintenance_check file to be in all caps
Add tests

* Create a standard and maintenance mode test sites
* Test that the standard site returns a response of 200
* Test that the maintenance mode site returns a response of 503
Merge branch 'master' of github.com:jisaacks/nginx_passenger-cookbook into jisaacks-master
Add `apt` recipe; Add `curl` to test-cookbook; Convert Berksfile to 3
Merge branch 'jisaacks-master'
0.3.0: Add support for maintenance mode

If `site` resource specifies a `maintenance_page`, traffic will be redirected
there if a given maintenance check file is present.  By default, we look for
`(dir)/IN_MAINTENANCE_MODE`, but a custom file can be specified with
the `maintenance_check` attribute.