docs: def yum_update(self, allow_reboot=False):
          """Do a yum update on the system.
  
          :param allow_reboot: If True and if a new kernel has been installed,
          the system will be rebooted
          """
          self.run('yum clean all')
          self.run('test -f /usr/bin/subscription-manager && subscription-manager repos --list-enabled',
                   ignore_error=True)
          self.run('yum repolist')
          self.run('yum update -y --quiet', retry=3)
          # reboot if a new initrd has been generated since the boot
          if allow_reboot:
              self.run('grubby --set-default $(ls /boot/vmlinuz-*.x86_64|tail -1)')
              default_kernel = self.run('grubby --default-kernel')[0].rstrip()
              cur_kernel = self.run('uname -r')[0].rstrip()
              if cur_kernel not in default_kernel:
                  self.run('reboot', ignore_error=True)
              self.ssh_pool.stop_all()