Rebuild initramfs on package upgrade (already done for Debian
previously) and store 1 into /var/lib/qubes/initramfs-updated. Then,
only add xen_scrub_pages=0 kernel option if
/var/lib/qubes/initramfs-updated is there (with "1" or greater number).
This way, if initramfs rebuild doesn't happen for any reason,
xen_scrub_pages=0 will not be added.
Fixes 456fe99 "Disable scrubbing memory pages during initial balloon down"
QubesOS/qubes-issues#1963
de2150e3d3