Add integration tests for fixed tree -> reward tree -> variable tree and reward tree -> variable tree.

[drewstone]

There are 2 potential integration test flows:

1. We start with a fixed deposit, move to another fixed deposit, claim a reward and add a commitment to the variable deposit tree, then move variable deposits around.

2. We start with a fixed deposit into the reward tree, claim the reward and add a commitment to the variable deposit tree, then, move variable deposits around.

We should have full flow tests of this including failing cases.