Multiple Sidekick functionality added.

[Rakhmanov]

Adding ability to update sidekick images.
In following format for multiple sidekicks: --sidekick nginx nginx:latest --sidekick node node:alpine
Or just one flag for single.

[Rakhmanov]

To test it you can use my dockerhub image.

This deployment step from my drone.yml:

deploy:
image: rakhmanov/drone-rancher
url: yourRancherAPIURL
access_key: ***
secret_key: ***
service: some/service
docker_image: php php
sidekick: nginx nginx:latest
sidekick: storage tianon/true

[josmo]

@Rakhmanov thanks for the PR, I'll take a look at it his week and merge it in :)

[Rakhmanov]

@josmo You are very welcome, let me know.