Make `images show` behave like other commands

Unlike all the other commands, if you did not supply an argument to
`images show` it would be an error.

For the majority of the show commands we implement the find all or warn
pattern where no arguments gives a detailed listing of everything and
arguments filter the code.
Make `lbs show` behave as other commands

Same issue as with images command. We were raising an error for empty
arguments in these cases but showing detailed listings in others.

This updates the command to show all load balancers or filter if args
are given.
Harmonise other show actions.

The earlier show actions for servers and users had the same
inconsistency with the newer commands. They would error with no args
rather than listing everything in details.

Since the newer behaviour is friendlier it is preferred.
Merge pull request #47 from brightbox/image_command_show_fix

Make `images show` behave like other commands