Pin SQLAlchemy to 0.7.x

0.7.10 has been released and is compatible with 0.7.x. Instead
of pinning to 0.7.9, simply pin to 0.7.x to avoid SQLAlchemy 0.8

Also sync the 0.7.x requirements to 0.7 (to be in sync with other
OpenStack core components)

Fixes: Bug #1153983

Change-Id: Ie20344e96f3d12e93695579adff0a0d9b4c1c516