Add debian into available distros for image building
Add debian into available distros for image building

the debian is supported for image build[0], but the docs missing
it, the ps to add it.

[0]: https://github.com/openstack/kolla/blob/master/kolla/common/config.py#L22

Change-Id: I4bbdb1a607566b4853c6767fca6401cc78576e95

openstack/kolla,stackforge/kolla,rahulunair/kolla,stackforge/kolla,openstack/kolla,rahulunair/kolla,stackforge/kolla