python3: Switch to mox3 instead of mox

In order to transition to a python 3.x compatible world,
lets switch to mox3 which is python 3.x compatible drop-in
replacement of mox.

Change-Id: Iaa22779cd516f842c9f70828f863f90ddae0bab5
Add release notes for 1.3.0a3

Change-Id: If97e1d695e498aac41aabbc1cea7cb9336b3b725
Merge "Add release notes for 1.3.0a3"