Stop `fig run` starting everything when a service has no links

This was thanks to the semantics of project.up(), which starts everything
if you pass it an empty list of service names. (That logic should
probably be moved out to main.py.)

Signed-off-by: Aanand Prasad <aanand.prasad@gmail.com>
Merge pull request #279 from orchardup/fix-run-with-no-links

Stop `fig run` starting everything when a service has no links