Create automatable test verifying checkpoint integrity after errors

We recently fixed a bug in WiredTiger checkpoint implementation, where a system error happening at a critical point during a checkpoint operation could lead to corruption in the block extent lists. We should add a test case the simulates failures and ensures that checkpoints are not corrupted.

The fix was in WT-2897.

An avenue for implementing this testing might be via a custom filesystem implementation that fails write operations occasionally during checkpoints.