Make token_provider_api contain token persistence

The token_provider_api now houses the token persistence manager
directly. A new token_api provider has been created that just
proxies to token_provider_api.persistence.

This is in support of deprecating use of token_api internal to
Keystone and migrating direct uses of token_api to gate through
the token_provider_api methods.

Uses of the token_api within the provider and provider drivers
has been lifted up to the token_provider_api manager and now
utilize the persistence manager directly.

Change-Id: I62cc1d5efbe0869fd0e501aaa9405ff0b0da0e5e
bp: non-persistent-tokens
Merge "Make token_provider_api contain token persistence"