condense credentials (ec2, v3, compute)

I like the idea of --type x509. We can pick a default type, I'd like 'cert' from the wtf-is-it standpoint (ec2 and x509 are pretty clear).

The --data option should be a filename or '-' for stdin. If it is required, maybe even read from stdin if --data is not supplied for the correct type.

Related patch: https://review.openstack.org/#/c/148466/

If you define "--type ec2", shouldn't really all arguments be optional? It should probably take the domain_id, user_id and project_id from the currently scoped token by default?

The typical consumer of Openstack services probably just wants to create an access key to use with Swift/S3 API or the Nova/EC2 API. And he/she problably have no idea on how to look up the various ID's needed, as there probably is no access to identity:list_domains/list_projects/list_users without special privileges.

@dag-stenstad, agreed they should get retrieved from the auth session. Additionally, an admin may want to create ec2 cred for a non-admin account.

Change abandoned by Steve Martinelli (<email address hidden>) on branch: master
Review: https://review.openstack.org/148466
Reason: abandon for now

Ticket 1418837 complains that the arguments to 'credential set' claim to be optional but in reality are required. The spec https://github.com/openstack/keystone-specs/blob/master/api/v3/identity-api-v3.rst#credentials-v3credentials says they are required too.

I have a change proposed https://review.openstack.org/#/c/226922/ enforcing that user, type, and data (aka blob) are all required. Should ec2 work differently?