Require oslo.config 1.2.0a2

Fixes bug #1182662

Commit 362bd7f switched us from using 'QUOTA' as a config file section
name to using 'quota'.

This broke backwards compatibility support for 'QUOTA' because the
version of oslo.config that has that compat support had not yet been
released. The gory details are summarized here:

  http://lists.openstack.org/pipermail/openstack-dev/2013-May/009448.html

Change-Id: I7826087147e0713edaaea85a72283998295e2281
Merge "Require oslo.config 1.2.0a2"