Rework the vboot_reference make system.

tests/gen_test_keys.sh

 #!/bin/bash
 
 # Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 #
 # Generate test keys for use by the tests.
 
 # Load common constants and variables.
 . "$(dirname "$0")/common.sh"
 
 # Generate RSA test keys of various lengths. 
 function generate_keys {
   for i in ${key_lengths[@]}
   do
+    if [ -f ${TESTKEY_DIR}/key_rsa$i.keyb ]; then
+      continue
+    fi
     openssl genrsa -F4 -out ${TESTKEY_DIR}/key_rsa$i.pem $i
     # Generate self-signed certificate from key.
     openssl req -batch -new -x509 -key ${TESTKEY_DIR}/key_rsa$i.pem \
       -out ${TESTKEY_DIR}/key_rsa$i.crt
     # Generate pre-processed key for use by RSA signature verification code.
     ${UTIL_DIR}/dumpRSAPublicKey ${TESTKEY_DIR}/key_rsa$i.crt \
       > ${TESTKEY_DIR}/key_rsa$i.keyb
   done
 }
 
 mkdir -p ${TESTKEY_DIR}
 generate_keys