Improved XenServer patching

Despite we already streamed the patches all the way along (download, unzip, upload on the fly at once), we still have ways to improve the patch fetching mechanism, since everything changed on XenServer 7.1 and 7.2!

Note that it was already optimized for XenServer 7.0 and before

It changed so much that we had to do it a bit less "optimized" way than expected:

So right now, you'll have only one stream for all:

• less bandwidth used
• faster to deploy
• still streamed in the whole process

And still, using just one click for your whole pool!