Allow RunIn on a paused Container

Docker-DCO-1.1-Signed-off-by: Glyn Normington <gnormington@gopivotal.com> (github: glyn)
Abstract uid and gid to FileOwner

uid and gid are Linux specific and so should not appear on the
Container interface.

Docker-DCO-1.1-Signed-off-by: Glyn Normington <gnormington@gopivotal.com> (github: glyn)