Go conventions are for interfaces to be defined on the receiver side,
and for producers to return concrete types. This patch changes the
constructor to return a concrete type.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
This will allow plugins to have custom typed endpoints, as well as
create/remove/update contexts with the exact same results as the main
CLI (thinking of things like `docker ee login https://my-ucp-server
--context ucp-prod)`
Signed-off-by: Simon Ferquel <simon.ferquel@docker.com>