Fix 'install_requires' warning when building with --install

[Roboterbastler]

When building the package with install space enabled (catkin config --install) I got the following warning:

Warnings   << mqtt_bridge:install /opt/enway/ws/logs/mqtt_bridge/build.install.001.log                                                                                                                    
/usr/lib/python2.7/distutils/dist.py:267: UserWarning: Unknown distribution option: 'install_requires'
  warnings.warn(msg)
cd /opt/enway/ws/build/mqtt_bridge; catkin build --get-env mqtt_bridge | catkin env -si  /usr/bin/make install; cd -

distutils apparently doesn't support 'install_requires', replacing it with setuptools (which is also matching the example in http://docs.ros.org/melodic/api/catkin/html/howto/format2/installing_python.html) fixes that.

[ledmonster]

thank you !!