feature: variables for scale: id, hostname

[ioggstream]

This patch enables parametric hostnames and commands when using scale
avoiding all bash variables expansion issues.

# docker-compose scale test=4
test:
  image: busybox:latest
  hostname: test-%%id%%
  command: runme.sh %%hostname%%

Signed-off-by: Roberto Polli robipolli@gmail.com

[StefanScherer]

@ioggstream +1 for that! I'm struggling giving another container an URL to a scaled container with the correct host name. I'll try your PR.

But the Jenkins Compose-PR build seems to have problems:

CONFLICT (content): Merge conflict in compose/service.py

Perhaps you have to rebase your PR.

[ioggstream]

@StefanScherer rebased and nosetesting... hopefully you'll have the patch in a while

[ioggstream]

@StefanScherer: Moved here #1131