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

tools/pip-requires

@@ -51,7 +51,7 @@ routes>=1.12.3
 rtslib>=2.1.fb27
 setuptools_git>=0.4
 simplejson>=2.0.9
-sqlalchemy>=0.7,<=0.7.9
+sqlalchemy>=0.7,<=0.7.99
 sqlalchemy-migrate>=0.7
 stevedore>=0.6
 suds>=0.4