yocto_recipe: add static method to get ROS_PYTHON_VERSION value
yocto_recipe: add static method to get ROS_PYTHON_VERSION value

* it will be used for creating context for conditional evaluations in rosdistro as well

Signed-off-by: Martin Jansa <77d25b640e536c950b8ae8cdd4f0574e3b263d04@lge.com>

ros-infrastructure/superflore,ros-infrastructure/superflore