aaa: Fix group name issues for legacy provider

Chagning format from: authz/a/b/c/d to: a/b/c/d@authz
to conform to the users format.
Removed specific code at rest-api that handled old format.

Change-Id: I8c1feed08e33156c794b230fa04f33f2ebd82240
Topic: AAA
Signed-off-by: Yair Zaslavsky <yzaslavs@redhat.com>