Work around that 'make-key' has rc 1 on success.

The 'make_key' script returns rc 1 on both failure and success, so work
around by ignoring exit code from that script.

sign-build

@@ -71,7 +71,7 @@ generate_keys () {
 
     mkdir $KEY_DIR
     for x in releasekey platform shared media; do \
-        ./development/tools/make_key $KEY_DIR/$x "$SUBJECT"; \
+        ./development/tools/make_key $KEY_DIR/$x "$SUBJECT" || true; \
     done
 }