Fix error code flag when using Python 3

[Dunedan]

When using Python 3 the error code flag was never set, thanks to the
division changes between Python 2 and Python 3.

The behavior before this commit was:

Python2:

>>> status_code = 403
>>> status_code / 100 == 4
True

Python3:

>>> status_code = 403
>>> status_code / 100 == 4
False

[haotianw465]

Actually if you look at https://github.com/aws/aws-xray-sdk-python/blob/master/aws_xray_sdk/core/models/entity.py#L89 whenever there is a status code set on segment/subsegment, the flags are set accordingly. I think that explains why https://github.com/aws/aws-xray-sdk-python/blob/master/tests/ext/botocore/test_botocore.py#L29 this test can pass on both python2/3. I think the logic on boto_utils.py is leftover code that should be completely removed. The entity class should be the central place to adjust the flags based on status code.

[Dunedan]

Ah, right. That explains why it wasn't caught earlier. I pushed a new commit to remove the flagging from boto_utils completely.

[haotianw465]

Hi, this looks good to me. Could you merge your two local commits into one so I can merge that single commit to the master?

[Dunedan]

Here you go. 😄