Account generator for identity v3

Extend account generator to work with identity v3 API and
credentials. To do so, replace a good chunk of the existing code
with the credential provisioning APIs of the dynamic credentials
provider. Add unit test coverage for the tool.

Depends-on: I9fcb3497387fb32f3e515cda44a1a105921a04c2

Closes-bug 1494293
Change-Id: I9970cb29ec4d448a381b4fe293fdfd91d8cfc17a
3 files changed