Remove unused cert db method.

nova.db.sqlalchemy.api contained a certificate_get() method that was
unused.  It was not in the main db.api.  This method was also the only
reference to CertificateNotFound, so remove that as well.

Change-Id: Iba9aece2302e2f175e5d60e48b23959885a81c8d
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

Specifically, when heat is enabled in tempest gating, the following
tests are failing:
- tempest.api.compute.test_auth_token.AuthTokenTestJSON.test_v3_token
- tempest.api.compute.test_auth_token.AuthTokenTestXML.test_v3_token

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

Fixes bug: #1190149

Change-Id: Ia0a2a48461593fdc0f5be57bcc9f364c3e3f8b66
Merge "Raise max header size to accommodate large tokens."
Merge "Remove unused cert db method."
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp