[wip/prf-gazebo-ros-pkgs] Set prf-gazebo-ros-pkgs available only for xenial.

This package is only available with xenial.

prf-gazebo-ros-pkgs/Makefile

@@ -16,6 +16,8 @@ CATEGORIES=	wip
 MASTER_REPOSITORY=	${MASTER_REPOSITORY_GITHUB}${ORG}/${NAME}.git
 CHECKOUT_VCS_OPTS+=	--recursive
 
+ONLY_FOR_PLATFORM= Ubuntu-16.04-%
+
 HOMEPAGE= 	${MASTER_SITE_GITHUB:=${ORG}/${ROSNAME}}
 MASTER_SITES=	${HOMEPAGE}/archive/