Add WSGIPassAuthorization to OAuth docs

OAuth headers will not be passed in if operating Keystone under
Apache. Mention this in the docs that are used to enable OAuth,
so a deployer can know it's a configuration setting in mod_wsgi.

Partial-Bug: #1392584
Change-Id: I12e734650d9428460522e6b8f04baf7325bfc778
Speed up memcache lock

Simplify sleep timeouts calculation removing progressive scale.

Closes-bug: #1395688
Change-Id: I0f1b620df9631a4b081e8c0be93d8a9b2d60e105
Merge "Add WSGIPassAuthorization to OAuth docs"
Merge "Speed up memcache lock"