Have ansible respect private_key_file option

The ansible command-line tool was ignoring the private_key_file option.

lib/ansible/utils.py

@@ -394,7 +394,7 @@ def base_parser(constants=C, usage="", output_opts=False, runas_opts=False,
         default=constants.DEFAULT_HOST_LIST)
     parser.add_option('-k', '--ask-pass', default=False, dest='ask_pass', action='store_true',
         help='ask for SSH password')
-    parser.add_option('--private-key', default=None, dest='private_key_file',
+    parser.add_option('--private-key', default=C.DEFAULT_PRIVATE_KEY_FILE, dest='private_key_file',
         help='use this file to authenticate the connection')
     parser.add_option('-K', '--ask-sudo-pass', default=False, dest='ask_sudo_pass', action='store_true',
         help='ask for sudo password')