Gracefully fail if invoked in `--privileged` mode

[grahamwhaley]

Description of problem

As described here: https://github.com/clearcontainers/runtime/blob/64a445eceebc839c142bc4aba6ff8e16702625bc/docs/limitations.md#docker-run---privileged We do not support --privileged mode in the runtime, but currently passing that argument will not fail, it will run the container - but potentially not give the functionality that the end user is expecting.

Expected result

If practicable, I'd like to see the runtime fail gracefully, and docker print out a useful error message. I don't know if the runtime can actually tell it was invoked in --privileged mode though - not sure if that information comes through directly in the json or not.