Catch filenotfound errors when launching etcd

uncloud/hack/db.py

@@ -53,7 +53,10 @@ class DB(object):
         # Can be set from outside
         self.prefix = prefix
 
+        try:
             self.connect()
+        except FileNotFoundError as e:
+            raise UncloudException("Is the path to the etcd certs correct? {}".format(e))
 
     @readable_errors
     def connect(self):