treewide: port everything to blockdev

This gets rid of most ad-hoc block device code, using blockdev for
everything. It also gets rid of diskfs for everything but tests. This
enables Metropolis to be installed on non-512-byte block sizes.

Change-Id: I644b5b68bb7bed8106585df3179674789031687a
Reviewed-on: https://review.monogon.dev/c/monogon/+/1873
Tested-by: Jenkins CI
Reviewed-by: Serge Bazanski <serge@monogon.tech>
diff --git a/metropolis/installer/test/testos/BUILD.bazel b/metropolis/installer/test/testos/BUILD.bazel
index 6eded96..8d5f267 100644
--- a/metropolis/installer/test/testos/BUILD.bazel
+++ b/metropolis/installer/test/testos/BUILD.bazel
@@ -17,7 +17,7 @@
 
 efi_unified_kernel_image(
     name = "kernel_efi",
-    cmdline = "loglevel=0 console=ttyS0 init=/init",
+    cmdline = "quiet console=ttyS0 init=/init",
     kernel = "//third_party/linux",
     verity = ":verity_rootfs",
 )