Remove unused package in requirement.txt

This patch is similar to https://bugs.launchpad.net/glance/+bug/1252344.

Currently wsgiref/passlib package exist in requirement.txt,
but I confirmed that they are unused in glance source by "grep" command.

I removed them to clean up.

Closes-bug: #1255826
Change-Id: Ibbc2f1d413efacd0c18ba16c9250ef08470667d1
DB migration changes to support DB2 as sqlalchemy backend

Implements bp db2-database

SQLAlchemy works in general, only changes needed to allow DB2
backend are these migration updates. The main difference
with DB2 is around index creation and constraints updates.

Change-Id: If5aa371328ef49ec93029ed15993871cfe5522cd
Merge "DB migration changes to support DB2 as sqlalchemy backend"
Merge "Remove unused package in requirement.txt"