Use conventional factory terminology

The Initialize method is responsible for creating a new Container instance
and calling it Create makes the factory pattern more obvious. Clearly
creating a Container instance involves initialising the instance.

Docker-DCO-1.1-Signed-off-by: Glyn Normington <gnormington@gopivotal.com> (github: glyn)
Merge pull request #83 from cf-guardian/create

Use conventional factory terminology