Add search option to not exit after goal found

[emichael]

Throughout the search tests now, we have the pattern:

searchSettings.maxTimeSecs(30);
searchSettings.addGoal(CLIENTS_DONE);
searchSettings.addInvariant(RESULTS_OK);
bfs(initSearchState);
assertGoalFound();

searchSettings.clearGoals();
bfs(initSearchState);

If the first bfs is not instant, this wastes significant time. It would be nice to have searchSettings.stopOnGoal() and instruct the search to continue even if it hits a goal-matching state (while still logging the goal-matching state). This will require some re-architecture of SearchResults and BaseJUnitTest as well as Search.java. Additionally, trace minimization should probably be done on the main thread instead of worker threads.