Use MDP database for simulator equivalence tests

Use MDP database for simulator equivalence tests

Changes the simulator equivalence tests to use the additional MDP
database introduced recently. This will allow to test algorithms
requiring additional MDP parameters more cleanly.

This also changes the MDP database behavior to overwrite default
parameters. This does not change any current behavior, as in the
current usage, no parameters are defined in both the default and
the additional parameter sets. Moving forward, it's more likely
that we will want to explicitly overwrite default parameters with
the additional database rather than have parameter redefinitions
silently fail.