When shutting down Mongrel, wait synchronously for stop.

The Mongrel tests on Ruby 1.9 were highly unreliable, sometimes failing
because they tried to bind a port that was already in use.

This turns out to be because the default shutdown mode is to asynchronously
stop workers - combined with the fact that our test made a TCP connection to
the service, but never actually completed the request.

That led to one thread that dangled, if the socket didn't close in a timely
fashion, and blocked up the listen port.

Instead, two things: first, wait for all threads to terminate (or 60 seconds
to pass) in the stop method, and second, use a full HTTP request to test, not
just a TCP connection with no content.

Signed-off-by: Daniel Pittman <daniel@puppetlabs.com>