主要是urllib3、pyOpenSSL版本太低，需要安装正确的版本。
pip show urllib3
pip show pyOpenSSL
pip uninstall urllib3
pip install urllib3==1.22
wget
ftp://ftp.ntua.gr/pub/linux/centos/7.5.1804/cloud/x86_64/openstack-ocata/common/pyOpenSSL-0.15.1-1.el7.noarch.rpm
rpm -Uvh pyOpenSSL-0.15.1-1.el7.noarch.rpm
参考：
https://www.irocky.top/articles/228
https://chengxuzhilu.com/1073.html
https://stackoverflow.com/questions/44397101/how-to-fix-urllib3-runtimeerror-requests-dependency-urllib3-must-be-version
之后再按照官网的安装步骤：
yum install epel-release
yum -y install yum-utils
yum-config-manager --enable rhui-REGION-rhel-server-extras rhui-REGION-rhel-server-optional
yum install certbot-apache
