Be more robust to missing keys.

fetcher.py

     self._prefix = prefix
 
 
+  def _read(self, key, **kwargs):
+    try:
+      node = self._client.read(self._prefix + key, **kwargs)
+      return node.value if node else None
+    except etcd.EtcdKeyNotFound:
+      return None
+
+
   def _read_recursive(self, key):
     try:
       return self._client.read(self._prefix + key, recursive=True)
 
 
   def wait_for_update(self):
-    original_time = self._client.read(self._prefix + '/_updated').value
+    original_time = self._read('/_updated')
     new_time = original_time
 
     while new_time == original_time:
       try:
-        new_time = self._client.read(self._prefix + '/_updated', wait=True).value
+        new_time = self._read('/_updated', wait=True)
       except etcd.EtcdWatchTimedOut:
-        new_time = self._client.read(self._prefix + '/_updated').value
+        new_time = self._read('/_updated')
       time.sleep(10)