The first attempt occasionally fails, probably due to a race with the
listener's startup.
Additionally, perform minor adjustments to the output written to stderr
to ensure it is properly flushed in the CI environment.
Since we restart Logstash to enable the UDP input prior to running this
test, we should also ensure it has successfully come back, otherwise we
start searching for the expected documents in Elasticsearch way too
early and often run into timeouts.
ci: Update Enterprise Search test for v3 index
App Search API keys are now encrypted in Elasticsearch, so we simply
ensure they exist and don't try to read their value.
Prevents the occasional connection timeout when the tool randomly picks
the IP of the ingress interface (usually 10.0.0.x/24) instead of the elk
interface (usually 10.0.1.x/24) in Swarm mode.
