Fix revert-resume Authentication Error

When we get private keys from the master node
there are two keys '/root/.ssh/id_rsa' and
 '/root/.ssh/bootstrap.rsa'.
An error occures when we try to use a wrong key,
but on the next iteration we use right one
and authentication passes.
So it's just cosmetic defect and patch fixes an exception
mechanism.

Change-Id: If167abc34f1c4060ab3b791204dc7245d06805d9
Closes-Bug: 1494856

devops/helpers/helpers.py

@@ -258,9 +258,11 @@ def connect(self):
                 return self._ssh.connect(
                     self.host, port=self.port, username=self.username,
                     password=self.password, pkey=private_key)
-            except paramiko.AuthenticationException as e:
-                logging.error("Authentication failed")
-                logging.exception(e)
+            except paramiko.AuthenticationException:
+                continue
+        if self.private_keys:
+            logging.error("Authentication with keys failed")
+
         return self._ssh.connect(
             self.host, port=self.port, username=self.username,
             password=self.password)