branch-obs: split the creation of OBS repos for -security, -updates and...

branch-obs: split the creation of OBS repos for -security, -updates and -backports in two steps due to OBS constraints

OBS refuses to create repo with nonexistent dependencies and because
we have circular dependencies between target and development,
we first need to create repo without dependencies and later re-add
dependencies.

Signed-off-by: Dylan Aïssi <dylan.aissi@collabora.com>