use zypper dist-upgrade instead of zypper update

I think it's better to use zypper dist-ugrade instead of
zypper update to make sure that packages of higher versions
maybe avaialble in the OBS repositories are applied.
zypper update will not apply them because a vendor-change
is necessary.

Change-Id: Ia735ec0a15e27c8e90955c388235cfc520cd21cb
Merge "use zypper dist-upgrade instead of zypper update"