to be py3 compatible. this addresses the failure of
```
2020-04-05T12:35:02.036 INFO:teuthology.run_tasks:Running task ssh_keys...
2020-04-05T12:35:02.050 ERROR:teuthology.run_tasks:Saw exception from tasks.
Traceback (most recent call last):
File "/home/teuthworker/src/git.ceph.com_git_teuthology_py3/teuthology/run_tasks.py", line 86, in run_tasks
manager = run_one_task(taskname, ctx=ctx, config=config)
File "/home/teuthworker/src/git.ceph.com_git_teuthology_py3/teuthology/run_tasks.py", line 64, in run_one_task
task = get_task(taskname)
File "/home/teuthworker/src/git.ceph.com_git_teuthology_py3/teuthology/run_tasks.py", line 28, in get_task
module = _import('tasks', module_name, task_name, fail_on_import_error=True)
File "/home/teuthworker/src/git.ceph.com_git_teuthology_py3/teuthology/run_tasks.py", line 52, in _import
0,
ImportError: No module named 'tasks.ssh_keys'
```
Signed-off-by: Kefu Chai <kchai@redhat.com>
from teuthology.orchestra import monkey
monkey.patch_all()
-from cStringIO import StringIO
+from six import StringIO
import os
from teuthology.orchestra import connection, remote, run
-from cStringIO import StringIO
+from six import StringIO
import contextlib
import logging
from teuthology import misc as teuthology
import re
from datetime import datetime
-from cStringIO import StringIO
+from six import StringIO
from teuthology import contextutil
import teuthology.misc as misc
from teuthology.orchestra import run