au-generator.zip: Add blockdev to au-generator.zip.

We need blockdev to rescan for for partitions if losetup --partscan doesn't
work.

BUG=None
TEST=Ran a butterfly-paladin tryjob.

Change-Id: Ibd0b66a940e21dbc6221e971512b160f6dacf8a7
Reviewed-on: https://chromium-review.googlesource.com/219480
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Tested-by: Gabe Black <gabeblack@chromium.org>
Commit-Queue: Gabe Black <gabeblack@chromium.org>
diff --git a/build_library/generate_au_zip.py b/build_library/generate_au_zip.py
index 830dab2..f0fb080 100755
--- a/build_library/generate_au_zip.py
+++ b/build_library/generate_au_zip.py
@@ -21,6 +21,7 @@
     '/bin/mount',
     '/bin/umount',
     '/sbin/losetup',
+    '/sbin/blockdev',
     # These are specific to our build.
     '/usr/bin/cgpt',
     '/usr/bin/delta_generator',