Issue 50164 - Add test for dscreate to basic test suite
    
    Bug Description:
    dscreate tests do not work properly when newer lib389 is used
    with older 389-ds-base versions.
    
    Fix Description:
    * Unset PYTHONPATH for dscreate if it's set to prevent clobbering system
    lib389.
    
    * Don't run dscreate_test on older versions, where instance-specific sysconfig
    env file is mentioned in systemd unit file. dscreate no longer creates it and
    causes dirsrv service fail to start.
    
    * Don't check for instance-specific sysconfig env file on removing the instance
    since it's no longer created.
    
    Fixes https://pagure.io/389-ds-base/issue/50164
    
    Reviewed by: mreynolds (Thanks!)