tests make dummy db setup/reset consistent

Move the setup/reset of the dummy DB into the test common base-class,
which ensures the setup/recent happens consistently (some tests setup
but then don't reset for example), and ensures there's always a clean
dummy DB per test.

Change-Id: I8e3bdd23399cb0d1d3c93daae66e6509b12b4e72
Merge "tests make dummy db setup/reset consistent"