Some tests used incorrect order assertEqual(observed, expected).
The correct order expected by testtools is
assertEqual(expected, observed).
This patch fix the issue in the modules magnum/tests/unit/db/. 、
magnum/tests/unit/object/. and magnum/tests/unit/service/. modules.
Change-Id: If193d8904ac4e4637e3ad97c8050696661cd6112
Partial-Bug: #1259292