Do not require secure file for nodepoold

We currently don't read anything from the secure file, so requiring
it seems pointless and confusing.

Change-Id: I1ab809d41bbfe709cd4ee34cbc9c481eed993868

nodepool/cmd/nodepoold.py

@@ -37,7 +37,6 @@ class NodePoolDaemon(nodepool.cmd.NodepoolDaemonApp):
                             default='/etc/nodepool/nodepool.yaml',
                             help='path to config file')
         parser.add_argument('-s', dest='secure',
-                            default='/etc/nodepool/secure.conf',
                             help='path to secure file')
         parser.add_argument('--no-webapp', action='store_true')
         return parser

nodepool/nodepool.py

@@ -1344,6 +1344,7 @@ class NodePool(threading.Thread):
 
     def loadConfig(self):
         config = nodepool_config.loadConfig(self.configfile)
+        if self.securefile:
             nodepool_config.loadSecureConfig(config, self.securefile)
         return config