feat(osfamilymap): add support for Gentoo

.yamllint

@@ -13,6 +13,7 @@ ignore: |
   node_modules/
   test/**/states/**/*.sls
   .kitchen/
+  syslog_ng/osfamilymap.yaml
 
 yaml-files:
   # Default settings

syslog_ng/osfamilymap.yaml

@@ -3,6 +3,7 @@
 ---
 Gentoo:
   package: app-admin/syslog-ng
+  service: {{ 'syslog-ng@default' if grains.init == 'systemd' else 'syslog-ng' }}
 
 Arch:
   service: syslog-ng@default.service