Block sqlalchemy migrate 0.9.2 as it breaks all of nova

This is breaking nova unit tests

Closes-Bug: #1368391
(cherry picked from commit 9c2d6f21854bc79f03095163b8133a9fec68f9f2)

Change-Id: Ic82d787e41f7b6d6153d3c6b19902cc11a1c43bb