Implement switch for updating pre-existing kickstart distributions

[stdevel]

Once kickstart distributions become outdated, installing newer packages from the Spacewalk repositories might fail. So it would be great to have a switch like -u / --update to update pre-existing kickstart distributions on the hard drive.

[pitkley]

Just as a hint for other people stumbling onto this issue, wondering if they have a way to update an existing tree even though this feature doesn't exist (yet). In my case I wanted to update my kickstart-tree for CentOS 7, which I initially created using:

mkelfs -o centos -r 7 -x x86_64 -c

To update the tree I simply changed the -c/--create-distribution to -f/--force:

mkelfs -o centos -r 7 -x x86_64 -f

This will trigger mkelfs to purge the old tree and download the new one, without touching the tree registered in Spacewalk. Please note that this is definitely not as optimal as a potential --update flag could be since the whole tree will be re-downloaded, even though some of the data might not have changed.