Symlinks have recently added some new keys to container listings. It's
very convenient to be able to see and reason about the extra information
in container listings.
Allowing raw json output is similar with what the client already does
for the info command, and it's forward compatible with any listing
enhancements added by future middleware development.
Change-Id: I88fb38529342ac4e4198aeccd2f10c69c7396704
936631eac6