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

Fixes: Bug #1153983

Change-Id: I1a2ea0c36161df15fd55e95a6679628d14858944
Merge "Pin SQLAlchemy to 0.7.x"