Our integration test runtime can be dramatically reduced by running mongod against an in-memory filesystem.  Anecdotal experience shows a reduction from 5 minutes to 2 minutes for server tests and 18 minutes to 3 minutes for replica set tests (run on my personal computer).

Using the storage engine `inMemory` causes some tests to fail.  Some of the failing tests appear to be caused by writeConcern settings that are not valid for the inMemory storage engine (docs) and they would be expected to fail.  Others might require debugging to determine the root cause of the failure.  I think the increased productivity is worth potentially skipping a few tests, since they will be run in CI against a wiredTiger server.

Acceptance Criteria

• Update the cluster_setup.sh script to launch servers with the `inMemory` storage engine.
• Add a new filter to our test runner to disable tests that cannot run on an inMemory storage engine.
• Skip any failing tests with the new filter.