Update netmgr, tasks, and applications to use isc_loopmgr

Previously:

* applications were using isc_app as the base unit for running the
  application and signal handling.

* networking was handled in the netmgr layer, which would start a
  number of threads, each with a uv_loop event loop.

* task/event handling was done in the isc_task unit, which used
  netmgr event loops to run the isc_event calls.

In this refactoring:

* the network manager now uses isc_loop instead of maintaining its
  own worker threads and event loops.

* the taskmgr that manages isc_task instances now also uses isc_loopmgr,
  and every isc_task runs on a specific isc_loop bound to the specific
  thread.

* applications have been updated as necessary to use the new API.

* new ISC_LOOP_TEST macros have been added to enable unit tests to
  run isc_loop event loops. unit tests have been updated to use this
  where needed.

lib/dns/rpz.c

@@ -1478,7 +1478,7 @@ dns_rpz_new_zones(dns_rpz_zones_t **rpzsp, char *rps_cstr, size_t rps_cstr_size,
 		goto cleanup_rbt;
 	}
 
-	result = isc_task_create(taskmgr, 0, &rpzs->updater, 0);
+	result = isc_task_create(taskmgr, &rpzs->updater, 0);
 	if (result != ISC_R_SUCCESS) {
 		goto cleanup_task;
 	}