Support python3_6 for ROS 1

[concavegit]

This addresses ros/ros-overlay#642

[allenh1]

@concavegit I seem to have made a mistake in assisting you! There's a couple more places to add it.

The example ebuild used for tests:

superflore/tests/ebuild/simple_expected.ebuild

Line 5 in 02b0dcd

PYTHON_COMPAT=( python{2_7,3_5} )

Test for the python version:

superflore/tests/test_ebuild.py

Line 156 in 02b0dcd

self.assertTrue('PYTHON_COMPAT=( python{2_7,3_5} )' in got_text)

After those two changes are done, this looks good to me.

[concavegit]

All right, added. Thanks for the guidance, it gave me a better idea of the project structure.

[allenh1]

lgtm -- thank you very much!