Modifying and testing add_labels

[davidalber]

This PR does two things:

• Removes the try-except logic from add_labels. I'm doing this because the add labels request returns 200 on success. Thus, we don't need the "look for 201 status code logic" here.
• Adds tests for add_labels.

I also verified the modified function manually.

>>> from newpr import add_labels
>>> add_labels(['a', 'b'], 'davidalber', 'highfive-test-repo', 2, 'davidalber', OAUTH_TOKEN)

>>> add_labels(['a', 'b'], 'davidalber', 'highfive-test-repo', 2, 'davidalber', FAKE_OAUTH_TOKEN)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "newpr.py", line 143, in add_labels
    api_req("POST", issue_labels_url % (owner, repo, issue), labels, user, token)
  File "newpr.py", line 86, in api_req
    f = urllib2.urlopen(req)
  File "/usr/local/Cellar/python/2.7.14/Frameworks/Python.framework/Versions/2.7/lib/python2.7/ur
llib2.py", line 154, in urlopen
.
.
.
urllib2.HTTPError: HTTP Error 401: Unauthorized

This is probably going to conflict with #111, after it is merged, so I'll need to rebase one of them.

[nrc]

Looks good, you're right though, it does need a rebase.

[davidalber]

Rebased! It doesn't seem to have kicked off a new build. 😕

[nrc]

Thanks!