Move listener initialization to cowboy_test
Fix two issues where listeners didn't get stopped properly
Make loop handlers work with SPDY

Adds a loop_handler test suite that runs all tests under HTTP, HTTPS,
SPDY each with and without the compress option enabled.

Fixes output filtering that used to filter more than it should have.
This forces us to parse the string sent by the emulator, which means
it's probably not perfect yet. But it should at least not hide errors
we want to see.

Fix a crash in the output filtering code that entirely disabled
output. Now when there is a crash the normal tty output is restored.

Handlers are now in test/handlers/ as they can be reused between
suites.

Only generate a single certificate for the whole ct run to speed
things up when we got many different test groups each needing
certificates.