Handling of long package lists for zypper

Unfortunately, zypper doesn't allow to install/remove packages via a list of packages stored in a file. Instead, the packages have to be passed via the command line.
When using long package lists, this may make the command line too long.
A solution to this problem is to limit the number of packages that are handled in a single zypper call, and to call zypper several times with batches of packages.
This pull request implements this improvement of the zypper module.