* Fix wrong suffix x86_64-linux-gnu in native python module shared library
* Python native module shared library is cross-compiled for correct
architecture but filename had an incorrect suffix 'x86_64-linux-gnu'.
As per python_cmake_module, if PYTHON_SOABI environment variable is not
defined, it'll query it from native's python sysconfig module.
https://github.com/ros2/rosidl/blob/master/python_cmake_module/cmake/Modules/FindPythonExtra.cmake
So adopt a solution similar to the one adopted below, where PYTHON_SOABI
is set explicitly for our specific build.
https://github.com/erlerobot/meta-ros2/blob/master/classes/ament.bbclass
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>