[RHEL/7] Version #2 of service_enabled (unix:file_test) template for systemd.

         Service is considered enabled if:
         * corresponding RPM is installed AND,
         * service in question is not masked AND,
         * service in question is enabled on boot time [*].

         Also apply that template against iptables service for testing.

[*] It's not needed to check if service isn't disabled at runtime, and
    simultaneously enabled on boot time, since this configuration is
    unreachable.