Always install python3 and its dev package

Some distros do not install python3/python3-devel with the minimal
install. F29 doesn't install -devel, and neither Centos 7 or 8
install either. This patch ensures that these packages get installed.

Ideally, PYTHON3_VERSION would be set *after* ensuring that python3
was installed, but it gets a little tricky with all of the includes.
This sets it to 3.6 as nothing uses 3.5 anymore.

Change-Id: I7bdfc408b7c18273639ec26eade475856ac43593
3 files changed