Support tiered tables in random_directio

We want to add tiered storage testing to as many of our stress tests as we can. This ticket involves adding tiered storage support and testing to test/csuite/random_directio.

We want to include things like:

• A configuration option specifying that the test should use tiered table(s)
• Configuration option(s) using different ways of triggering flush operations (periodically from the application, periodically managed by WT, wait vs. nowait, timeout, etc.)
• It will use the dir_store because that supports direct I/O.