[RHEL/7] Update form of RHEL-7 service disable / enable check macros
         (from chkconfig to systemctl)
[RHEL/7] Update 'Disable telnet Service' XCCDF rule description
         (default service-disable-macro can't be used in this case)

Version #2: Replace <code> with <tt>. Thanks Shawn.
Version #3: Fix s/xinet.d/xinetd.d/ typo. Thanks Gabe.
Merge pull request #240 from iankko/version_3_rhel7_update_service_macros

[bugfix] [RHEL/7] Version #3 - Update form of RHEL-7 service disable / enable check macros