Make sure ssh retries on paramiko.SSHException

We are occasionally seeing paramiko raise a SSHException which is
causing tempest to fail out, but on a constrained devstack environment
its possible that there are network or other performance issues, so we
want to keep retrying on an SSHException just like we retry on a
paramiko.AuthenticationException.

Attempt at Closes-Bug: #1253896

Change-Id: I4293f9a47a6d524ced0d09eb67a52c5ed1ad361e
(cherry picked from commit 31a91a605a25f578b51a7bed2df8fde5c5f49ffc)