Add missing tests for iscsi_* methods

There was no tests in test_db_api for iscsi_*
methods.

Bug 1187367 found.

blueprint db-api-tests

Change-Id: Ia554e6030307a0c4f0510ab74fe0881ee160f743
Unset all stubs before running other cleanups.

Cleanup callbacks are run in reverse order so all stubs unsetting
should be added at the end of the cleanup list.

Fixes bug 1185004

Change-Id: I5ad3ea2cdce663aaeae6b7cc2cb9c5dac9d12435
Merge "Add missing tests for iscsi_* methods"
Merge "Unset all stubs before running other cleanups."