efivarfs, osimage: fix boot entry handling

efivarfs was updated to handle partition UUIDs in the mixed-endian
format [1], enabling it to produce correct boot entries. Its interface
was changed in the process, leading to further changes in osimage.

In addition, BootEntry.Marshal will replace any backslash with a
forward slash in the EFI executable path.

[1] https://en.wikipedia.org/wiki/Universally_unique_identifier#Encoding

Change-Id: Ib8300e01fd1664d0c08bb033b1dc36addb925b20
Reviewed-on: https://review.monogon.dev/c/monogon/+/456
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
diff --git a/metropolis/node/build/mkimage/osimage/BUILD.bazel b/metropolis/node/build/mkimage/osimage/BUILD.bazel
index d9cacae..88f1dd8 100644
--- a/metropolis/node/build/mkimage/osimage/BUILD.bazel
+++ b/metropolis/node/build/mkimage/osimage/BUILD.bazel
@@ -11,5 +11,6 @@
         "@com_github_diskfs_go_diskfs//disk:go_default_library",
         "@com_github_diskfs_go_diskfs//filesystem:go_default_library",
         "@com_github_diskfs_go_diskfs//partition/gpt:go_default_library",
+        "@com_github_google_uuid//:go_default_library",
     ],
 )