pushimage: Log unused --sign-types arguments

Log all sign-types args that are not used to upload a signing instruction.

BUG=None
TEST=bin/pushimage '--board=brya' --sign-types recovery factory hps_firmware
TEST=-n gs://chromeos-image-archive/brya-release/R100-14517.0.0

Change-Id: Ib9edb162fb13807ff62de5076ebcba7ccb558d3f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/3460705
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Evan Benn <evanbenn@chromium.org>
Tested-by: Evan Benn <evanbenn@chromium.org>
diff --git a/scripts/pushimage.py b/scripts/pushimage.py
index dfaf656..4d224a5 100644
--- a/scripts/pushimage.py
+++ b/scripts/pushimage.py
@@ -502,6 +502,12 @@
           _AddToFilesToSign(image_type, dst, suffix)
 
     logging.debug('Files to sign: %s', files_to_sign)
+    unused_sign_types = set(sign_types or []) - set(
+        x for x, _, _ in files_to_sign)
+    if unused_sign_types:
+      logging.warning('Some sign types were unused: %s',
+                      ' '.join(unused_sign_types))
+
     # Now go through the subset for signing.
     for image_type, dst_name, suffix in files_to_sign:
       try: