CentOS7に入れたLet's EncryptでImportError

CentOS7でLet's Encryptを利用しているサーバで下記エラーになりました。
どうも[AWS コマンドラインインターフェイス](https://aws.amazon.com/jp/cli/)を導入すると、Let's Encryptとpythonがバッティングして
下記のようなエラーを出してそう。

### エラー
```
Traceback (most recent call last):
  File "/bin/certbot", line 9, in <module>
    load_entry_point('certbot==0.27.1', 'console_scripts', 'certbot')()
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 378, in load_entry_point
    return get_distribution(dist).load_entry_point(group, name)
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 2566, in load_entry_point
    return ep.load()
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 2260, in load
    entry = __import__(self.module_name, globals(),globals(), ['__name__'])
  File "/usr/lib/python2.7/site-packages/certbot/main.py", line 21, in <module>
    from certbot import client
  File "/usr/lib/python2.7/site-packages/certbot/client.py", line 16, in <module>
    from acme import client as acme_client
  File "/usr/lib/python2.7/site-packages/acme/client.py", line 36, in <module>
    requests.packages.urllib3.contrib.pyopenssl.inject_into_urllib3()  # type: ignore
  File "/usr/lib/python2.7/site-packages/urllib3/contrib/pyopenssl.py", line 118, in inject_into_urllib3
    _validate_dependencies_met()
  File "/usr/lib/python2.7/site-packages/urllib3/contrib/pyopenssl.py", line 153, in _validate_dependencies_met
    raise ImportError("'pyOpenSSL' module missing required functionality. "
ImportError: 'pyOpenSSL' module missing required functionality. Try upgrading to v0.14 or newer.
```

### 対応

```
# pip install --upgrade pip
# pip install requests --ignore-installed
# pip install --upgrade --force-reinstall 'requests==2.6.0'
```

### エラー2

後日再度エラーが発生。
やはりawscliとcertbotがライブラリ競合してそう。
上記対応やっても解消しなかったため、あえなくyumからインストールし直ししました。

#### 2-1エラー

```
# certbot
Traceback (most recent call last):
  File "/bin/certbot", line 9, in <module>
    load_entry_point('certbot==0.36.0', 'console_scripts', 'certbot')()
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 378, in load_entry_point
    return get_distribution(dist).load_entry_point(group, name)
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 2566, in load_entry_point
    return ep.load()
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 2260, in load
    entry = __import__(self.module_name, globals(),globals(), ['__name__'])
  File "/usr/lib/python2.7/site-packages/certbot/main.py", line 20, in <module>
    from certbot import client
  File "/usr/lib/python2.7/site-packages/certbot/client.py", line 14, in <module>
    from acme import client as acme_client
  File "/usr/lib/python2.7/site-packages/acme/client.py", line 37, in <module>
    requests.packages.urllib3.contrib.pyopenssl.inject_into_urllib3()  # type: ignore
  File "/usr/lib/python2.7/site-packages/urllib3/contrib/pyopenssl.py", line 118, in inject_into_urllib3
    _validate_dependencies_met()
  File "/usr/lib/python2.7/site-packages/urllib3/contrib/pyopenssl.py", line 160, in _validate_dependencies_met
    "'pyOpenSSL' module missing required functionality. "
ImportError: 'pyOpenSSL' module missing required functionality. Try upgrading to v0.14 or newer.
```

#### 2-2 対応

```
# pip install --upgrade pip
# pip install requests --ignore-installed
# pip install --upgrade --force-reinstall 'requests==2.6.0'
```

#### 2-3 対応してもエラー

```
# certbot
Traceback (most recent call last):
  File "/bin/certbot", line 5, in <module>
    from certbot.main import main
  File "/usr/lib/python2.7/site-packages/certbot/main.py", line 20, in <module>
    from certbot import client
  File "/usr/lib/python2.7/site-packages/certbot/client.py", line 14, in <module>
    from acme import client as acme_client
  File "/usr/lib/python2.7/site-packages/acme/client.py", line 40, in <module>
    urllib3.contrib.pyopenssl.inject_into_urllib3()
AttributeError: 'module' object has no attribute 'pyopenssl'
```

### 対応2

yumからインストールし直ししました。

```
# yum --enablerepo=epel remove certbot python-certbot-apache
# yum --enablerepo=epel install certbot python-certbot-apache
# pip install --upgrade pip
# pip install --upgrade --force-reinstall 'requests==2.6.0'
```

// pythonで動いてるawscliも動くか確認。（たまにエラー出るため）

```
# aws
```

### 情報源

https://github.com/certbot/certbot/issues/5534#issuecomment-364549029
https://qiita.com/morohoshi/items/05949674e000402c253c