sftp: add a more descriptive error on mkdirs (iterative#2554)

* sftp: add a more descriptive error on mkdirs

Fix iterative#2535

* sftp: raise exception instead of logging one

dvc/remote/ssh/connection.py

@@ -106,7 +106,10 @@ def makedirs(self, path):
                 # Since paramiko errors are very vague we need to recheck
                 # whether it's because path already exists or something else
                 if e.errno == errno.EACCES or not self.exists(path):
-                    raise
+                    raise DvcException(
+                        "unable to create remote directory '{}'".format(path),
+                        cause=e,
+                    )
 
     def walk(self, directory, topdown=True):
         # NOTE: original os.walk() implementation [1] with default options was