Remove redundant code from magnum.test.utils
Remove redundant code from magnum.test.utils

Some codes in magnum.tests.utils is redundant. The Database class
has been defined in magnum.test.unit.db.base. get_dummy_session
and create_models_from_data are not used by other codes. So we
just remove it.

Change-Id: Ib91e1f61f0032221fe4f45237b5ea8cf09d13564
Closes-Bug: 1476458

eshijia/SUR,eshijia/magnum,eshijia/magnum,eshijia/SUR,Tennyson53/SUR,dimtruck/magnum,openstack/magnum,jay-lau/magnum,dimtruck/magnum,ChengTiesheng/magnum,ramielrowe/magnum,paulczar/magnum,ramielrowe/magnum,sajuptpm/magnum,openstack/magnum,mjbrewer/testindex,paulczar/magnum,ffantast/magnum,Tennyson53/magnum,mjbrewer/testindex,Alzon/SUR,Alzon/SUR,mjbrewer/testindex,sajuptpm/magnum,ffantast/magnum,ArchiFleKs/magnum,ChengTiesheng/magnum,ddepaoli3/magnum,Tennyson53/SUR,annegentle/magnum,ArchiFleKs/magnum,annegentle/magnum,ddepaoli3/magnum,Tennyson53/magnum