This patch implements the HTTP transport.
Some notes:
- Consider not having a version for the transport implementation
since we already have one for the API definition.
- Consider moving transport implementations under a private package
since they're not suppose to be inherited nor imported. To load a
transport users have to use `transport.get_transport(_for)`
Partially-Implements blueprint python-marconiclient-v1
Change-Id: Ie2c70b3c160c5a331bd79765b2f4d69433e5bd73
fcccf5e1ba