Moving eventlet.hubs.use_hub call up

Under the design concept of eventlet, we need to call
eventlet.hubs.use_hub() before the application starts
doing any I/O. And it makes custom log handlers register
correct event listeners.

Closes-bug: 1247889
Change-Id: I3d43021c8cb6ed630123781f3686d62e5159edfc
Signed-off-by: Zhi Yan Liu <zhiyanl@cn.ibm.com>
Use `_LW` where appropriate in db/sqla/api

Moved some of the sqlalchemy driver code to use the `i18n._*`
translation functions.

Change-Id: Ib78dbf435982289eae45014876c4da6258631c05
Merge "Use `_LW` where appropriate in db/sqla/api"
Merge "Moving eventlet.hubs.use_hub call up"