Raise h11 and h2 exceptions in debug mode

[Quentin Pradet]

While porting the urllib3 test suite to use Hypercorn, my initial progress was very slow because I could not figure why Hypercorn was sometimes closing the connection. Turns out that this is the default behavior when h11 or h2 raise an exception, but that makes debugging much more difficult. I'm now using the following patch: urllib3@d1719f8 which helps a lot.

Would you be open to make this the default behavior when using debug mode?