Due to the architecture of how memcache gets deployed with each
unit of keystone, its possible for the cache on different units
to become consistent.
This results in non-deterministic behaviours depending on which
keystone unit services an API request.
Disable caching by default to ensure consistency and security
within a deployment; Operators may choose to enable caching and
can reduce the impact of cache unit inconsistency by tuning the
expiration configuration options from the default of 600 seconds.
Change-Id: I3601a8db6a0cf56d5482bba3bc35046d64cca452
Closes-Bug: #2089616
d2e42f1a6f