Catch all exceptions when failing to parse an Authorization header.

Clients can send garbage Authorization headers that will trigger more
than just a ValueError. We want to treat any error as an auth failure,
so now we just catch all exceptions and log them.

Reviewed at https://reviews.reviewboard.org/r/6288/
Clean up a bunch of PEP-8/pyflakes problems.

This change fixes up a bunch of relatively straightforward errors. Most of
these have to do with particulars of whitespace and indentation.

Testing done:
Ran unit tests.

Reviewed at https://reviews.reviewboard.org/r/6284/