Adds Cloud Audit (CADF) Support for keystone authentication

This restores context passing to the manager layer which was originally
included to support auditing / logging (which we haven't supported until
now), and was later removed to support caching. However, we don't have
any reason to cache the results of authenticate() and it needs to be
audited. -dolphm

Change-Id: I2d43617f66fa2b23221dcfa4f7e935f64e458e1c
Implements: bp audit-event-record
DocImpact
Merge "Adds Cloud Audit (CADF) Support for keystone authentication"