Add missing tests for s3_image_* methods

There was no tests in test_db_api for s3_image_*
methods.

Add tests to ensure that all works.

blueprint db-api-tests

Change-Id: I906025f4c5178b26c222fb28d5c3b220e00ae79c
Merge "Add missing tests for s3_image_* methods"
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp