Permissions checks broken on master

[pietroalbini]

After updating bors to the latest master in the rust-lang/rust repository, we saw a few problems:

• Users in the reviewers list could post comments without any problem
• Users in the try list received a "you're not a reviewer" message
• Normal users received both "you're not a reviewer" and "you can't use try" messages

I think the cause of that is #149. Before that PR, the verify_auth calls were "configured" at the start of process_command and then called when they were actually needed. Instead, now the verify_auth calls are directly executed at the start of process_command, which means bors check if the user is a reviewer even if they send a simple comment without any command.

The simple solution to this issue is to reintroduce functools.partial in auth checks.

cc @alexrs @jdm @alexcrichton

[alexrs]

@pietroalbini Oh, my bad. Thanks for pointing the problem out. I'll create a PR reintroducing the functools.partial in auth checks and I'll try to create some tests to avoid this problem in the future.
We're working on refactoring Homu to make it testable (unfortunately, with the current code, it's really hard to test), so please, if you detect any other problem, report it!

[alexrs]

@pietroalbini I have created this PR that should solve the problem. #151

[pietroalbini]

Thank you so much!