Only store modified properties to python state files

This updates the python state file code to only store properties
which have modified values. This reduces the clutter in python
state files.

Change-Id: Ie1a7115771f79b1b7f30bd9e21bd39a66bae5d75
Merge topic 'only-store-modified-properties' into next

9c46abb Only store modified properties to python state files