Flag an error if key file can't be found

If no local key file can be found, flag an explicicit error to prevent
keys from silently going amiss.

Change-Id: Iec899193154131c68885ceae84ae34f99e5e157d
diff --git a/scripts/pws b/scripts/pws
index 202d983..6812f78 100755
--- a/scripts/pws
+++ b/scripts/pws
@@ -923,6 +923,8 @@
         user_keyfile = File.join('keys', "#{uid}.key")
         if File.file?(user_keyfile)
           keyring.write(File.read(user_keyfile))
+        else
+          puts "No key file found for user " + uid
         end
       end
     end