move generation of ephemeral database names (used in perf/unit testing) to a...

move generation of ephemeral database names (used in perf/unit testing) to a higher level and out of core code.  also, emphemeral database cleanup is now a responsibility of the harness running the software (test harness, or run_locally.js).  This fixes race conditions in unit tests that restart daemons (closes #557) and simplifies running local performance tests (issue #504)