Rename __init__.py to create_volume.py

This commit is the first step of creating packages structure for
flows. This change is required to preserve git history of renamed files
for change I63473f549f0c501fe0f373830bc1080239d01892

Change-Id: Ib5ed0e9196fa7bf4fd0b69a13c90e40c360ad8ef
Merge "Rename __init__.py to create_volume.py"