rockylinux : create machine-id early

Somewhere between the upstream container
rockylinux/rockylinux:8.6.20220515 and the latest release, systemd
started to be pre-installed in the container.

With <= 20220515 installing the kernel-core package would end up
pulling in systemd.  As part of the systemd package installation, the
/etc/machine-id file is created and populated.

The kernel package post-install steps install the kernel with
/bin/kernel-install; this is responsible for copying the kernel
binaries into /boot.  It does this based on the machine-id, and it
seems its failure case with a blank machine-id is to simply skip
copying the kernels into /boot.  To compound this problem, it seems
our bootloader installation doesn't notice that we don't have a kernel
installed, so we end up building an unbootable image.

Testing is/was showing us this; but as rocky is non-voting and this
occured at a random time (rather than in response to a dib change) I
think it slipped by us.

To work around this, create the machine-id early in the container.  We
already have paths that remove the machine-id from final images.

Change-Id: I07e8262102d4e76c861667a98ded9fc3f4f4b82d

diskimage_builder/elements/rocky-container/containerfiles/8

@@ -5,3 +5,8 @@ RUN dnf install -y findutils util-linux sudo python3 NetworkManager
 RUN systemctl unmask console-getty.service dev-hugepages.mount \
     getty.target sys-fs-fuse-connections.mount systemd-logind.service \
     systemd-remount-fs.service
+
+# /etc/machine-id needs to be populated for /bin/kernel-install to
+# correctly copy kernels into /boot.  We will clear this out in the
+# final image.
+RUN systemd-machine-id-setup