Fixed some python2->3 string issues

[foozlevazquez]

• httplib2 breaks if headers are not strings: https://github.com/jcgregorio/httplib2/blob/master/python3/README
  fixes: Attribute error thrown in gcloud/exceptions.py #653
• exception message was confusing and broken as byte string.

[coveralls]

Coverage remained the same at 100.0% when pulling 59fff73 on foozlevazquez:master into 56f60bb on GoogleCloudPlatform:master.

[dhermes]

@foozlevazquez How did you test that the failures in #653 are passing? Can you add unit tests?

Also, can you git merge --squash into a single commit? For a 4-line change, 5 commits is too noisy.

PS I see you've signed the CLA, @googlebot is useful sometimes!

[dhermes]

@foozlevazquez Is this the httplib2 reference you are making:

To successfully use http2lib for Python 3, you absolutely must
understand the following sentence:

** THE RESPONSE HEADERS ARE STRINGS, BUT THE CONTENT BODY IS BYTES **

[foozlevazquez]

@dhermes Regarding #653, I tested it by hand on the test case that I had when I ran into these bugs in the first place. I'll look into writing some tests and squashing the commits as well.

Regarding httplib2, yes.

[dhermes]

Great! Let me know if you need some help and I can make some suggestions / lend a hand.

[dhermes]

@foozlevazquez What's up?

[foozlevazquez]

@dhermes
I'm working on a cleaned resubmittal.

Also, I realized that #653 has a root cause of some python2-3 string crap that is taking place in oauth2client here - So I'm working on a pull-request for that as well.

Essentially I'm having to untangle a set of fixes I made in a hacking frenzy... :)

Thanks for checking.

[dhermes]

That's great! I can help on the oauth2client side as well, or we can loop in @craigcitro

The people who added Python 3 support there weren't actually running unit tests (eek!) and I tried to fix most of it in:
googleapis/oauth2client#87

[craigcitro]

+1 to fixing any/all issues in oauth2client. @nathanielmanistaatgoogle or @soltanmm is likely to be quicker than me with the code reviews.

[foozlevazquez]

The origin of this all is some code that simply does the following:

from gcloud import storage

conn = storage.get_connection('myproj')
[x for x in conn.get_all_buckets()]

The example above dies with the infamous oauth2client.client.AccessTokenRefreshError: invalid_grant exception. i.e. #653
But, this code works under Python2.7, which lead me to find that the headers were being composed incorrectly in oauth2client, specifically here.

I've initiated googleapis/oauth2client#136 to fix and test the above.

To fix problems with make_exception and api_request, I've submitted #675.