Create a diskless containerVM

[corrieb]

For end-to-end testing the Port Layer exec redesign #1043, combined with TCE #1044, it would be extremely useful to have a diskless containerVM. This would allow us to test without any network or storage dependencies. A statically linked application could be copied into a RAMdisk via the tether.

It's unclear whether the app binary could be copied during initialization. If so, then we could trigger the entrypoint just like if there was a disk attached. If it has to be copied in after initialization, then we'd have to have to treat it like an exec. The lifecycle of the container would still need to be tied to the lifecycle of the application.

This should hopefully be very simple to implement. We just don't attach a disk and then get the initialization script in the ISO to start up in a particular mode - either because it can detect there's no disk attached - or because of some guestinfo setting.

[mdubya66]

Should this remain open. Seems the ship has sailed or is there more research needed?

Marking low as not a 1.1 requirement

[hickeng]

Adding this back in to refactor portlayer - not because it's a core requirement for containerVMs, but because it's needed by vic-machine if that's to use the portlayer to create the endpoint.

This addresses the bootstrap requirement of having a means to place data on a vmdk without having an endpointVM already running.

An alternative approach would be a slightly different pl.storage impl to use when self-hosted in vic-machine, that instead of attaching a disk to prepare an image instead authors a vmdk directly and uploads that to the expected location.