<oo-admin-ctl-groups> Bug 964205 - fix stopuser(), add "repair" command

Modified stopuser() to check if the cgroup for the specified user has
already been stopped, and echo a useful message if that is the case
instead running cgdelete and generating "file not found" noise

Added a new command to oo-admin-ctl-cgroups called
"repair". This command identifies users which lack a cgroup and
creates a cgroup for them. It can be called with an optional username
argument (or a quoted space-separated list of usernames) to restrict
the action to a specific subset.

@markllama