With this change, when we attempt to boot with an initramfs and fail,
initrdless_boot_fallback_triggered is set to non-zero in the grubenv.
This value can be checked after boot by looking in /boot/grub/grubenv
or by using the grub-editenv list command.
Boot without an initramfs by default if running a custom kernel
Initramfs-less boot, which is a boot optimization, should only be
applied where we know it could work for users and provide an improved
boot boot experience; images with custom kernels are candidates for
that.
Generic cloud images with the linux-generic kernel are not able to
boot without an initramfs. Previously, these images attempted to boot
without an initramfs, would fail, and then retry with an initramfs.
This slows the boot and is confusing behavior.
functions: stop removing systemd-detect-virt unconditionally in undivert_grub
One can call divert_grub; replace_kernel; undivert_grub. And
replace_kernel will call into force_boot_without_initramfs, which
under certain conditions can call divert_grub &
undivert_grub. Resulting in undivert_grub called twice in a row.
When undivert_grub is called twice in a row it wipes
systemd-detect-virt binary from disk, as the rm call is unguarded to
check that there is something to divert if systemd package is
installed. And if the systemd package is not installed, it does not
check that systemd-detect-virt file is in-fact what divert_grub has
created.
Add a guard to check that systemd-detect-virt is the placeholder one,
before removing it.
LP: #1902260
(cherry picked from commit 096a00f40459187719840ccad99e86c7ade2ec12)