Upgrade WebOb to 1.2.3

Upgrade WebOb to 1.2.3

The version of WebOb being used in OpenStack was more than
1 year old. This change updates to the latest stable release.

Upgrading WebOb resolves a version conflict between OpenStack
and Pecan, the web framework used by the Ceilometer team for
version 2 of the ceilometer API.

Refer to http://docs.webob.org/en/latest/news.html
for the list of changes between 1.0.8 and 1.2.3.

Fixes Bug #1092227

Change-Id: I07707607ae2067a567e11c347cddda9c7e6bcef7