cli: Add double dash to run usage

This is so we can use flag-like arguments in the command without them
being parsed by docopt, e.g.:

flynn -a example run -e bash -- -c 'echo $FOO'

Signed-off-by: Lewis Marshall <lewis@lmars.net>
host/cli: Add Entrypoint and Cmd to inspect output

Signed-off-by: Lewis Marshall <lewis@lmars.net>
Merge pull request #502 from flynn/cli-tweaks

CLI tweaks