We find that the --pastebin option to pytest sometimes fails with "HTTP
Error 400: Bad Request". We're still investigating the exact cause of
these errors, but in the meantime, a failure to upload to the pastebin
service should probably not crash pytest and cause a test failure in the
continuous-integration.
This patch catches exceptions like HTTPError that may be thrown while
trying to communicate with the pastebin service, and reports them as a
"bad response", without crashing with a backtrace or failing the entire
test suite.