Skip signing key check in some cases

Test: th
Bug: 205657204

Change-Id: I3a2fc886cfb3fe3d53619bfb8fe84aa799d80de3

tools/releasetools/ota_from_target_files.py

@@ -1473,6 +1473,11 @@ def main(argv):
           "build/make/target/product/security/testkey")
     # Get signing keys
     OPTIONS.key_passwords = common.GetKeyPasswords([OPTIONS.package_key])
+
+    # Only check for existence of key file if using the default signer.
+    # Because the custom signer might not need the key file AT all.
+    # b/191704641
+    if not OPTIONS.signapk_path:
       private_key_path = OPTIONS.package_key + OPTIONS.private_key_suffix
       if not os.path.exists(private_key_path):
         raise common.ExternalError(
@@ -1531,8 +1536,5 @@ if __name__ == '__main__':
   try:
     common.CloseInheritedPipes()
     main(sys.argv[1:])
-  except common.ExternalError:
-    logger.exception("\n   ERROR:\n")
-    sys.exit(1)
   finally:
     common.Cleanup()