Fix connector interface not being exposed for docker+machine and docker-autoscaler executors

What does this MR do?

The docker executor implements InterativeTerminal and Connector interfaces.

• docker-autoscaler was not exposing either of these implementations via its executor wrapper.
• docker+machine was not exposing the Connector implementation via its executor wrapper.

Why was this MR needed?

Advertises to the rest of Runner that InterativeTerminal and Connector are implemented.

What's the best way to test this MR?

• Use docker-autoscaler with a simple step. Before this change it hangs. After this change, it works.

What are the relevant issue numbers?

Closes #39165 (closed) Closes #37860 (closed)