Remove shared net namespace and hosts file; use links instead
Fix: volumes defined in the image should live in the group dir too
Fix some nitpicky stuff about docker groups

1. Grammar
2. Commands not listed in global command list, which made discovery
difficult.
3. No YAML tags defined for some fields in group.yml.
4. COMMAND => SUBCOMMAND
5. Padding in subcommand list was not enough for "containers"

Docker-DCO-1.1-Signed-off-by: Nathan LeClaire <nathan.leclaire@docker.com> (github: nathanleclaire)