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
tests remove wr_delete_after decorator

This decorator was used for test cleanup before we set up a clean
dummy DB environment for every test, so it's no longer required

Change-Id: I1b0a27d64c298892048f39ac0cf6a39ae4b3076d
Merge "tests make dummy db setup/reset consistent"
Merge "tests remove wr_delete_after decorator"