This will get us more debug info in the logs if it happens again

Introduced CelluloidTest as a test class for all tests that depend on
Celluloid being up and running.

Turns out without this nickserver will not respond to multiple concurrent requests.

This way the logs do not interfere with test output

We handle these errors nicely in the dispatcher and have tests for that.
Tests should fail or err out when running into exceptions we are not
handling yet. But for these it's better to just skip.

Turns out http.rb does not support celluloid i/o andymore and we were not making
use of it anyway.

Here's what https://github.com/httprb/http/wiki/Thread-Safety says:
(NOTE: this gem previously supported Celluloid::IO, but that support was removed to add the current timeout backend. It may be added back in a future version)

So now we have a plain http.rb adapter and use that as the default.
This prevents actors from crashing in the adapter (as we don't have any).