hooks: disallow SDK packages installing into /boot

This directory only makes sense for boards, not the SDK.

BUG=None
TEST=SDK builders passes

Change-Id: I50502ebaf24080679b89ba29e1e088b79eaebb83
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/2113298
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Alex Klein <saklein@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
diff --git a/hooks/filesystem-sanity.py b/hooks/filesystem-sanity.py
index b5770b0..a749528 100755
--- a/hooks/filesystem-sanity.py
+++ b/hooks/filesystem-sanity.py
@@ -24,13 +24,13 @@
 # always bind mounted with the host distro, and we don't want to pollute them.
 # Those are: /dev
 VALID_ROOT = {
-    'bin', 'boot', 'etc', 'home', 'lib', 'lib32', 'lib64', 'media',
+    'bin', 'etc', 'home', 'lib', 'lib32', 'lib64', 'media',
     'mnt', 'opt', 'proc', 'root', 'run', 'sbin', 'sys', 'tmp', 'usr', 'var',
 }
 
 # Paths that are allowed in the / dir for boards.
 VALID_BOARD_ROOT = {
-    'build', 'dev', 'firmware',
+    'boot', 'build', 'dev', 'firmware',
     # TODO(): We should clean this up.
     'postinst',
 }