Fix broken nginx-unicorn support
addresses puppet-puppet issue 119 by switching from using the default
location in the vhost to using an explicitly defined location, in
order to avoid the default headers that cannot be unset on the default
location.

Add beaker tests to test for this problem
Note that the beaker tests for this pass, but there are still failures.
I think it's better to get this fixed and add tests rather than blocking
on fixing everything.

Also updates rack case statement to support puppet 3.7.x
Merge pull request #122 from danieldreier/nginx_unicorn_fix

Fix broken nginx-unicorn support
Switch default beaker nodeset to Debian
Ubuntu is still available but the default is Debian 7
Separate out server acceptance tests
passenger, thin, unicorn, and webrick can be tested independently
This implies differences to how tests are run, so documentation was
updated
The advantage here is no chance of bleed-over between test cases,
whereas the previous way required imperfect automated cleanup between
test cases.
This also permits testing one thing at a time to save a little bit of
time. Unfortunately, it also means that testing all cases requires
considerably longer because a new VM must be provisioned for each case.