Split and fix live db tests

With this commit, it's now possible to only run live tests (i.e. on real
database) on certain backend. Typically, I don't have HBase installed, so
now I can run the live tests against MongoDB and MySQL only very easily.

Change-Id: I0e584b8243abc27ab9f027fdea17dc6c1192c62d
Signed-off-by: Julien Danjou <julien@danjou.info>
Merge "Split and fix live db tests"