nit: uc <object> ls should not take args (or use them)

[miekg]

Slight inconsistency:

 uc volume ls            
NAME           DRIVER   MACHINE
atomdns_data   local    machine-9q7y
db_data        local    machine-9q7y
% uc volume ls db_data   
NAME           DRIVER   MACHINE
atomdns_data   local    machine-9q7y
db_data        local    machine-9q7y

the right thing is to filter on the cmd-line args for consistency , although

% docker volume ls atomdns_atomdns_data  
docker: 'docker volume ls' accepts no arguments