解决方法

yum install certbot
pip install --upgrade --force-reinstall 'requests==2.6.0' urllib3

Traceback (most recent call last):
  File "/usr/bin/certbot-2", line 9, in <module>
    load_entry_point('certbot==0.22.0', 'console_scripts', 'certbot')()
  File "/usr/lib/python2.7/site-packages/pkg_resources/__init__.py", line 570, in load_entry_point
    return get_distribution(dist).load_entry_point(group, name)
  File "/usr/lib/python2.7/site-packages/pkg_resources/__init__.py", line 2751, in load_entry_point
    return ep.load()
  File "/usr/lib/python2.7/site-packages/pkg_resources/__init__.py", line 2405, in load
    return self.resolve()
  File "/usr/lib/python2.7/site-packages/pkg_resources/__init__.py", line 2411, in resolve
    module = __import__(self.module_name, fromlist=['__name__'], level=0)
  File "/usr/lib/python2.7/site-packages/certbot/main.py", line 17, in <module>
    from certbot import account
  File "/usr/lib/python2.7/site-packages/certbot/account.py", line 17, in <module>
    from acme import messages
  File "/usr/lib/python2.7/site-packages/acme/messages.py", line 7, in <module>
    from acme import challenges
  File "/usr/lib/python2.7/site-packages/acme/challenges.py", line 11, in <module>
    import requests
  File "/usr/lib/python2.7/site-packages/requests/__init__.py", line 58, in <module>
    from . import utils
  File "/usr/lib/python2.7/site-packages/requests/utils.py", line 32, in <module>
    from .exceptions import InvalidURL
  File "/usr/lib/python2.7/site-packages/requests/exceptions.py", line 10, in <module>
    from .packages.urllib3.exceptions import HTTPError as BaseHTTPError
  File "/usr/lib/python2.7/site-packages/requests/packages/__init__.py", line 95, in load_module
    raise ImportError("No module named '%s'" % (name,))
ImportError: No module named 'requests.packages.urllib3'