automation: use zypper dup in tumbleweed dockerfile

automation: use zypper dup in tumbleweed dockerfile

The 'dup' command aligns the installed packages with the packages
found in the enabled repositories, taking the repository priorities
into account. Using this command is generally a safe thing to do.

In the context of Tumbleweed using 'dup' is essential, because package
versions might be downgraded, and package names occasionally change.
Only 'dup' will do the correct thing in such cases.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>