Generic transactions test cases will run in a new test suite called core_txns, that will run the tests in jstests/core/txns against a single node replica set. We separate this from the basic core suite since transactions are only supported on replica sets. By default, since these new tests will be under the core directory, they will run on all the same suites and variants that the existing core tests run under. Transactions, however, will only be supported on WiredTiger storage engines and, initially, only on replica sets. We will use a uses_transactions file tag to appropriately ignore these tests from the proper variants and passthrough suites. This will require any new generic transaction test that goes into this directory to be tagged in this way.

We should also migrate any existing transactions test into this new directory/suite.