docker 内执行 systemctl 报错 解决方案： Failed to get D-Bus connection: Operation not permitted

分析：
find / -name systemctl              # 查找 systemctl 命令，发现下面两个，分别执行下面两个，发现第一个没有权限，因此
/usr/share/bash-completion/completions/systemctl
/usr/bin/systemctl

解决方案
yum -y install systemd firewalld net-tools ; yum -y install openssh openssh-server openssh-clients 
# 安装必备工具包
chmod +x /usr/share/bash-completion/completions/systemctl
# 给 systemctl 权限
rm -rf /bin/systemctl ; ln -s /usr/share/bash-completion/completions/systemctl /bin/systemctl
# 重新引用systemctl 工具