m/n/c/update: implement kexec-based activation

As we've had some issues with EFI-based slot activation and enterprise
server firmware is extremely slow, this implements kexec-based
activation. This just kexecs into the freshly-installed slot instead of
rebooting. It still updates the BootOrder on successful boot to allow
cold-boots if the server crashes or loses power, but no longer uses the
NextBoot mechanism to boot into the new slot once (this is taken care of
by kexec).

Change-Id: I6092c47d988634ba39fb6bdd7fd7ccd41ceb02ef
Reviewed-on: https://review.monogon.dev/c/monogon/+/2021
Reviewed-by: Serge Bazanski <serge@monogon.tech>
Tested-by: Jenkins CI
diff --git a/metropolis/node/BUILD.bazel b/metropolis/node/BUILD.bazel
index fe48cce..597c5d8 100644
--- a/metropolis/node/BUILD.bazel
+++ b/metropolis/node/BUILD.bazel
@@ -123,7 +123,7 @@
 
 efi_unified_kernel_image(
     name = "kernel_efi",
-    cmdline = "console=ttyS0,115200 console=ttyS1,115200 console=tty0 quiet rootfstype=erofs init=/init",
+    cmdline = "console=ttyS0,115200 console=ttyS1,115200 console=tty0 quiet rootfstype=erofs init=/init loadpin.exclude=kexec-image,kexec-initramfs",
     initrd = [":ucode"],
     kernel = "//third_party/linux",
     os_release = ":os-release-info",