httpinstance: Restore SELinux context of session_dir /etc/httpd/alias
    
    The session directory /etc/httpd/alias/ could be created with the wrong
    SELinux context. Therefore httpd was not able to write to this directory.
    
    Fixes: https://pagure.io/freeipa/issue/7662
    
    Related-to: 49b4a057f1b0459331bcec2c8d760627d00e4571 (Create missing
                /etc/httpd/alias for ipasession.key)
    
    Reviewed-By: Christian Heimes <cheimes@redhat.com>