fix known issues in 3 automated tests
    
    1) opensmtpd-and-similar test:
    The opensmtpd service needs to be started before an email can be sent
    via the mailx command. The original order led to the following error:
    
      /root/dead.letter 17/564
      s-nail: ... message not sent
    
    2) deny-rules test:
    The deny-rules test intentionally triggers SELinux denials. These
    SELinux denials should not be reported as errors or warnings.
    
    3) systemd-modules-load-and-similar test:
    Not all kernel modules required by the RDMA services are available
    on all machines. To avoid unnecessary failures, the test phase
    devoted to bz#1942267 will be skipped on such machines.
    
    The automated tests should be fixed now.