Changed from hardcoded http codes to using constants from httplib
Changed from hardcoded http codes to using constants from httplib

Changed from hardcoded 304 and 401 http codes to using the NOT_MODIFIED and UNAUTHORIZED constants from httplib for better readability.

Testing Done:
RBTools nose test results - all passed fine

----------------------------------------------------------------------
Ran 166 tests in 3.966s

OK (SKIP=50)

Bugs closed: 3841

Reviewed at https://reviews.reviewboard.org/r/7625/

davidt/rbtools,reviewboard/rbtools,datjwu/rbtools,datjwu/rbtools,davidt/rbtools,reviewboard/rbtools,datjwu/rbtools,davidt/rbtools,reviewboard/rbtools