系统连接到 RHN 失败并出现"The certificate is expired"或者 "certificate verify failed" 报错

Issue

在 RHEL 5 上运行的系统使用 yum 或者使用 RHN 进行系统注册时，出现下述报错:
~~~
"The certificate is expired. Please ensure you have the correct certificate and you system time is correct."
~~~

• rhn-virtualization-host 的 cron job 生成下述日志:

  up2date_client.up2dateErrors.SSLCertificateVerifyFailedError: The certificate is expired. Please ensure you have the correct certificate and your system time is correct.
  

• rhn_check失败并出现类似下述报错:

  [('SSL routines', 'SSL3_GET_SERVER_CERTIFICATE', 'certificate verify failed')]
  

• 每隔2秒在日志中出现"ssl certificate failed verification"

• 不能通过 yum 安装或者更新软件包，并出现下述报错:

  up2date_client.up2dateErrors.SSLCertificateVerifyFailedError: The certificate is expired. Please ensure you have the correct certificate and your system time is correct.
  

• rhn_register 失败并出现下述报错:

rhn_register ERROR: can not find RHNS CA file: /usr/share/rhn/RHN-ORG-TRUSTED-SSL-CERT
The certificate /usr/share/rhn/RHNS-CA-CERT is expired. Please ensure you have the correct certificate and your system time is correct.