Description of trust configuration options

Configuration option = Default value	Description
[trust]
allow_redelegation = False	(BoolOpt) Enable redelegation feature.
driver = sql	(StrOpt) Entrypoint for the trust backend driver in the keystone.trust namespace.
enabled = True	(BoolOpt) Delegation and impersonation features can be optionally disabled.
max_redelegation_count = 3	(IntOpt) Maximum depth of trust redelegation.