Optimize loading pattern list

[lslezak]

Problem

• Loading the list of available patterns takes too long time, about 10 seconds
• It turned out that for loading the patterns libzypp is called almost 700x in a Tumbleweed installation!

Solution

• Use the attribute preloading in to reduce the number of needed libzypp calls to just a single call

Testing

• Tested manually, now the list of patterns is obtained in a fraction of a second, there is just a single libzypp call