asap-tools: SystemExportersService.stop leaves blackbox_exporter running on the coordinator #908

SystemExportersService.start (asap-tools/experiments/experiment_utils/services/system_exporters.py) starts blackbox_exporter on the coordinator node. stop runs killall node_exporter; killall blackbox_exporter; … only on get_node_range(include_coordinator=False), so the coordinator's blackbox_exporter is never stopped. The teardown script calls the same stop, so it misses it too.

Seen in both RQE-frontend CloudLab runs on 2026-10-15 (#886): after each run, node0 still had blackbox_exporter running from that run and it had to be killed by hand. The next run starts another one on the same port.

Fix: in stop, also killall blackbox_exporter on get_coordinator_node().