fix backup parameters for pve-qemu-kvm 1.4-4

bump version to 2.3-11

depend on pve-qemu-kvm 1.4-4
add offline backup for templates
disable hotplug by default

This reverts commit 6c52b6794e10fb5e4bdad2b417b60496afc067a5

Testing revealed that this has too many side effect, so we do not want
to change that for the 2.3 release.