Remove the limitations on docker images

[sciabarracom]

In OpenWhisk you can use generic docker image (--docker) but unless the images are in the runtimes.json they have scalability limited to 2.

I believe this limitation is because originally docker images where pretty inefficient but since there is action loop this is no more the case.

I propose just to remove this limitation allowing images created with --docker run as the others so people can use any custom runtime without having to redepoli with a new runtimes.json

[kcexn]

Is this limitation imposed by OpenWhisk or by the docker container? I've deployed blackbox containers before that implement the action interface without this concurrency limitation.

[style95]

IIRC, there is no scalability limitation on docker actions.
@sciabarracom Could you elaborate more on this?