SSH: Fail to push binary data
## Description
I get an error when trying to push generated model files to my remote over ssh.

## General steps to reproduce:
* Init dvc repository
* Add an ssh remote
* Train the model using `dvc run`
* DVC push
The error I get is : `Error: Failed to push data to the cloud: sequence item 0: expected str instance, bytes found`

## More details
* First, I am just beginning to use DVC, so I may have missed a step.
* The output of `dvc run...` is a directory, which contains several files. Some are text files, but others are binary files.


diff --git a/dvc/remote/ssh.py b/dvc/remote/ssh.py
index a04f45419..8c5ebde07 100644
--- a/dvc/remote/ssh.py
+++ b/dvc/remote/ssh.py
@@ -152,7 +152,7 @@ class RemoteSSH(RemoteBase):
         stderr.close()
 
         if stdout.channel.recv_exit_status() != 0:
-            err = ''.join(stderr_chunks)
+            err = b''.join(stderr_chunks).decode('utf-8')
             msg = 'SSH command \\'{}\\' failed: {}'.format(cmd, err)
             raise DvcException(msg)
 
['dvc/remote/ssh.py']