Add cleanup scripts (#1025)

* Run cleanup scripts if they're there

* Cleanup script, add to build script

* okay

* I'm all shelled out

* Comment for future greg

code/tools/pkgresources/python_cleanup_scripts/cleanup.sh

@@ -0,0 +1,11 @@
+#!/bin/sh
+
+set -e
+
+if [ -f "/usr/local/munki/python" ]; then
+    /bin/rm /usr/local/munki/python
+fi
+
+if [ -d "/usr/local/munki/Python.framework/Versions/3.7" ]; then
+    /bin/rm -r /usr/local/munki/Python.framework/Versions/3.7
+fi