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 0.7.8 (to be in sync with other
OpenStack core components)

Fixes: Bug #1153983

Change-Id: I6f47e7d27fcf0c7271bb2c91a4615ef0bb5e2643
Merge "Pin SQLAlchemy to 0.7.x"