DISPATCH-2200 Add basic TCP adaptor microbenchmark w/ 2 routers (#1303)

* reset the dispatch pointer; just for cleanliness, not actually necessary to do
* basically working tests; except one was getting stuck (before I rebased the PR)
* move test setup around; introduce helper to run router in a subprocess
* delete the two routers in a thread benchmark case; that cannot work due to dispatch's use of global variables
* call qd_entity_cache_free_entries; this should not be forgotten
4 files changed