rostest: add catkin devel space the CMAKE_FIND_ROOT_PATH

Rostest depends on its own package and therefore needs to search
in the devel space for the rostestConfig.cmake during native
build.

| CMake Error at /.../usr/share/catkin/cmake/find_program_required.cmake:5 (message):
|   rostest not found
|

Signed-off-by: Stefan Herbrechtsmeier <stefan@herbrechtsmeier.net>

recipes-ros/ros-comm/rostest_1.9.41.bb

@@ -8,3 +8,5 @@ DEPENDS = "boost rosunit-native"
 require ros-comm.inc
 
 S = "${WORKDIR}/ros_comm-${PV}/tools/${BPN}"
+
+OECMAKE_EXTRA_ROOT_PATH_class-native = "${OECMAKE_BUILDPATH}/devel"