vm based args in spec??

There was an existing comment in the VM PR located here that was not resolved before merge:

https://github.com/opencontainers/runtime-spec/pull/949#discussion_r178318374

The overall issues is why do vm args need to be specified in the spec when the hypervisor is the one being invoked to read/process the spec.