Python 3 support

[imsickofmaps]

Currently an issue arises from requests_testadapter:

BytesIO.__init__(self, stream)
TypeError: 'str' does not support the buffer interface

We have worked around this in seed-stage-based-messaging tests by encoding it:

adapter = RecordingAdapter(json.dumps(response).encode('utf-8'))

This would also require an updated importing of url_parse:

try:
    from urllib.parse import urlparse
except ImportError:
    from urlparse import urlparse

[hodgestar]

@gsvr Which bits of the go-http-api code does this refer to?

[gsvr]

@hodgestar go_http/tests/test_metrics.py, for example https://github.com/praekelt/go-http-api/blob/develop/go_http/tests/test_metrics.py#L95

[hodgestar]

Could you open a pull request to add Python 3 to Travis and then we can review and sort out issues there?

[imsickofmaps]

@hodgestar done as requested

[hodgestar]

We will also need to update the fakes module from the go-contacts-api package.

[hodgestar]

Noting that http://python-future.org/compatible_idioms.html is a good palce to start for this work (and depending on the future module is probably sensible).