Add /etc/default support to the unicorn init script.

This makes it possible to override the environment variables in case of
custom set ups. This is needed for the ansible set up of linuxfr test
environment.

See https://github.com/nud/ansible-linuxfr
Replace 'source' with '.' in init.d/unicorn

This was a bash-ism.
Add /etc/default support to the img init script.
Merge branch 'master' of https://github.com/nud/admin-linuxfr.org

Conflicts:
	init.d/img