Fixing a number of small issues in the cppsuite test framework

There are a number of bugs / usability issues that can be fixed relatively quickly:

1. Reset sweep cursor on end of sweep.
2. Reset insertion cursor after insert / update.
3. Share the thread_context’s session with the transaction context. So users don't get confused as to which session is being used.
4. Fix hs_cleanup using the wrong session.
5. Verify the final collection in the validation component.
6. Only print on thread count != 0 in the workload generator.