repository: Add test to exercise CreateFromBundle with transactions

We recently got a bug report about CreateFromBundle() seemingly misbehaving when transactions are enabled. Symptoms are that voters drop out at seemingly random steps with weird error messages like e.g. "Unable to read current working directory". While this likely indicates some kind of external race, I still took the opportunity to write a test verifying that CreateFromBundle() works as expect with transactions enabled and that the votes are in fact computed deterministically.