filesystem-layout: make /var check more strict

We only banned subdirs previously.  Now ban it from being created at all.

BUG=b:187699610
TEST=CQ passes

Change-Id: I221dc8ecbdb31faf4e19f62a662a1bee54f86c85
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/3626128
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Sergey Frolov <sfrolov@google.com>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/hooks/filesystem-layout.py b/hooks/filesystem-layout.py
index 9c34ac3..43071f4 100755
--- a/hooks/filesystem-layout.py
+++ b/hooks/filesystem-layout.py
@@ -221,7 +221,7 @@
       ret = False
 
   # Special case /var due to so many misuses currently.
-  if has_subdirs(os.path.join(root, 'var')):
+  if os.path.exists(os.path.join(root, 'var')):
     if atom in BAD_VAR_PACKAGES:
       logging.warning('Ignoring known bad /var install for now')
     elif os.environ.get('PORTAGE_REPO_NAME') == 'portage-stable':