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

Unfortuantely '<0.8' matches '0.8.0b2', which is what we don't want.
Therefore pinning it to '<=0.7.99' instead.

Change-Id: I14eef50b5a423140421c6e8fe0a5242c2f676fa4
Merge "Pin SQLAlchemy to 0.7.x"