Move default creds to cred_provider

Credential types available in configuration, and how to parse
them and validate them is currently embedded in the Credentials
class hierarchy.

Move the entire logic to cred_provider, in preparation for the
migration of the auth module to tempest-lib.

The pre-provisioned account credential provider relied on
the list of configured field to find the hash for a set of
credentials. Changed that to use the list of attributes with
which the credentials were initially setup.

Change-Id: Ic3ff15799f016277e6eb59c53cf8f24f6a7be9c9
10 files changed