Update identity_group for 2.0.0

Replace calls to the sdk cloud layer with proxy layer calls where
appropriate.

Ensure module return values are converted into dict.

General refactoring to bring module more in line with collection
conventions.

Expand tests to assert idempotency and presence of return values.

Rename test role to identity_group to match module name.

Change-Id: I06fe28f77431bb151d85c8d9cd924a1634d85d98