Raise max header size to accommodate large tokens

The max header is exceeded in the following scenario
- Auth tokens built with a keystone v3 API catalog
- A catalog with approximately 8 or more endpoints defined

An equivalent fix will be required for all projects which use
eventlet.wsgi.

Copied from https://review.openstack.org/#/c/33362/

Closes-Bug: 1190149

Change-Id: I3fcb196b25a7a477b799c8dfa2ff5115977ca06d
(cherry picked from commit aa1ba1f0176af286506e4188628e5acbb8f7f0e6)
Merge "Raise max header size to accommodate large tokens" into stable/havana