Refactoring of 'DataGenerator' classes for identity V2 and V3

Variables self.test_user, self.test_tenant, self.test_project,
self.test_role and self.test_email were removed because all these
values can be taken from the corresponding resources.

Change-Id: I67d437c5244c4648002fbc6c843b59ae54e18bca
6 files changed