[bugfix] [RHEL/7] Update form of RHEL-7 service disable / enable check macros in shorthand2xccdf XSLT transformation

This change updates the form of:
* service-disable-macro,
* service-enable-macro,
* service-disable-check-macro,
* xinetd-service-disable-check-macro, and
* service-enable-check-macro

in order they to start using the form to read as ```# systemctl ...``` rather than ```# chkconfig ...```

Also update the 'Disable telnet Service' XCCDF rule description not to use the service-disable-macro (since the default form can't be used for telnet service on RHEL-7. We need a custom one for telnet).

Tested on RHEL-7 & works as expected.

Please review.

Thanks, Jan.