Prior to this commit, whenever the user selected the default kernel in
a VM's "Advanced Settings" dialog in Qubes Manager, the
"uses_default_kernel" flag would not be saved as expected. Instead of
the intent to use the default kernel version for the VM in the future,
the VM would be stuck with the specific kernel version and not any new
future default kernel versions.
This issue occurs because the "kernel" property setter for the QubesVm
class resets the "uses_default_kernel" member variable to False, and
Qubes Manager sets the "uses_default_kernel" property before setting the
"kernel" property.
Resolve this issue by making sure that the "uses_default_kernel"
member variable of the VM in question is set after the "kernel" member
variable.