* add a functions.sh file containing functions used by all three
container types, ImageBuilder, SDK and rootfs.
* allow SDK branch tags for other branches than `master`. This allows
testing of release SDK versions
* Fix handling of special snapshot versions like `21.02-SNAPSHOT`
Future commits will move `docker-download.sh` and `docker-build.sh` do
`functions.sh`.
Signed-off-by: Paul Spooren <mail@aparcar.org>
Paul Spooren