discover a mechanism to provide "rootless" containers

[mwartell]

It would be good to provide container users with container management that doesn't require root on the hosting system.

This is a stub issue with considerable refinement needed about the semantics of "rootless"

[davidslater]

Good discussion of issues: https://jtreminio.com/blog/running-docker-containers-as-current-host-user/

[christopherwoodall]

Possible duplicate of 1029.

[mwartell]

Fixed in #1786