Add bin/heat-manage to flake8 checks

Change-Id: I917e5b0aa571f2fced7df6a4818f32ce4b5f1561
Use Python 3.x compatible except construct

Python 3.x deprecated excecpt x,y. Use except x as y,
which works with any Python version >= 2.6

Change-Id: I264049ee41e75bcedea86adf7c2011c343f47ddb
Merge "Use Python 3.x compatible except construct"