Run wtperf stress testing against all maintained branches

1. Move wtperf configs for correctness stress jobs into a bench/wtperf/stress directory.

2. Change the wiredtiger-test-wtperf Jenkins job to iterate through all configs in that directory rather than hard-coding which ones to run.

3. Backport the stress configs to mongodb-3.0.

4. Delete the wiredtiger-test-wtperf-mongodb-* jobs.