run all as namespaced root

this purges the 'vcap' user from the codebase, and no longer permits creating
privileged processes.

the 'privileged' flag should be removed from the run API and moved to
container creation, where it will result in uid 0 being mapped to uid
0 outside of the container, and a user not being created for it.

also, the run API should probably be extended to support running processes as
a given user. right now you can only run as root (namespaced or not).