brew CI: use correct python and set PYTHONPATH (#1197)

Signed-off-by: Steve Peters <scpeters@openrobotics.org>

jenkins-scripts/lib/project-default-devel-homebrew-amd64.bash

@@ -88,10 +88,17 @@ fi
 
 if [[ -n "${PIP_PACKAGES_NEEDED}" ]]; then
   brew install python3
+  # reset command hash since python3 has already been invoked in this script
+  hash -r
   rm -rf ${WORKSPACE}/venv
   python3 -m venv ${WORKSPACE}/venv
   . ${WORKSPACE}/venv/bin/activate
   pip3 install ${PIP_PACKAGES_NEEDED}
+  # For python 3.X, our formulae install python bindings to
+  # ${HOMEBREW_PREFIX}/lib/python3.X/site-packages
+  # so add that folder to PYTHONPATH
+  python_minor_version=$(python3 -c 'import sys; print(sys.version_info[1])')
+  export PYTHONPATH=${HOMEBREW_PREFIX}/lib/python3.$python_minor_version/site-packages:$PYTHONPATH
 fi
 
 if [[ -z "${DISABLE_CCACHE}" ]]; then