[ci] Update CI container repository links

because I moved the project to another place so that it is easier to follow a common namespace for new base systems

- https://build.opensuse.org/project/show/OBS:Server:Unstable:container:Leap:42.3
- https://build.opensuse.org/project/show/OBS:Server:Unstable:container:SLE12:SP3
- etc...