Fix updated_at column of sqlalchemy tables
Fix updated_at column of sqlalchemy tables

The column updated_at does not update its value after the refactoring
made in 687ec913790653f79badc8f5d656c86792e94271.

Closes-Bug: #1457309
Change-Id: Iff45f386b5dc8efc3fe82ca3b1e961a0c23d7ac7

openstack/taskflow,junneyang/taskflow,jimbobhickville/taskflow,openstack/taskflow,pombredanne/taskflow-1,pombredanne/taskflow-1,junneyang/taskflow,jimbobhickville/taskflow