Add support for including background/perpetual workloads. Background/perpetual workloads should be done as background threads in resmoke.py and don't need any special handling other than ensuring adequate documentation in our internal wiki.

Also, add a new hook to drop all DBs and collections after every FSM test. When running in "the same" DB Or "same collection" FSM modes, pass the DB or collection that are not dropped to the new cleanup hook. CleanupOption of not dropping certain DBs will be taken into account as needed.

The new hook will be used in place of CleanEveryN to avoid the overhead of spinning up a large cluster multiple times.