Move support to Docker API v1.21

[AHelper]

Since networking is causing issues all around, I'm going to be making changes that may break compatibility with existing docker-gen configurations, however will address networking changes in v1.21, hopefully adding backwards compatibility to older docker versions.

• Remove all deprecated variables in RuntimeContainer that were deprecated in API v1.21 as part of the NetworkSettings (EndpointID, Gateway, GlobalIPv6Address, GlobalIPv6PrefixLen, IPAddress, IPPrefixLen, IPv6Gateway and MacAddress)
• Emulate a Network for pre-v1.21 Docker APIs.
• Update any tests that may rely on these removed fields.

Note: This really can't rely on pre-v1.21 as docker 1.7 has experimental support for network, however I don't know if the API worked then or if it should be supported.