Implement HTTP Transport

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