Mb2 shared output directory: allow to disable zypper distribution update

[rinigus]

Indeed, contamination between the builds can be prevented with snapshots. And it is a great feature.

However, the issue experienced here is within a build of a single package. So, in my case, while building droid-hal-version-h8324:

• zypper dup pulls in droid-config-XXXX and, as a result, droid-system-apollo and droid-system-apollo-h8314. The latter was by chance and, in theory, same could be provided by droid-system-apollo-h8314 (pay attention to the number behind h!)

• zypper install of dependencies on the line after that in mb2 script finds out that actually droid-system-apollo-h8324 is needed and that conflicts with installed h8314 system-apollo package.

This would all be prevented if zypper dup would be absent. Hence my request.