Doubled slash, a missing comma, and IoT-Agent readiness

[kzangeli]

Three unrelated defects, each of which stops a reader part-way.

1. A doubled slash

One request is written as http://localhost:1026//ngsi-ld/v1/entities/, from a URL variable that isn't there. A strict broker answers 400 Invalid URL Path rather than silently treating it as /ngsi-ld/v1/entities/.

2. A missing comma

"temperature": {
  "value": 16,
  "unitCode": "CEL"
  "observedAt": "2022-03-01T15:00:00.000Z"
}

The whole entityOperations/update?options=replace request is rejected as invalid JSON.

3. The tutorial cannot start: IoT-Agent readiness

waitForIoTAgent loops while the HTTP code is 000, so it stops waiting as soon as the port answers anything — including the 503 the agent serves while still initialising. IoT-Agent, IoT-Agent-JSON and Big-Data-Spark already wait on the container health status; this brings it into line.

And link-devices POSTs several ~30 KB device batches with no retry, under set -e. The agent intermittently closes the connection without replying — curl exit 52, "empty reply from server" — most often on the batch immediately after provision-devices. One such reply then kills the script silently, leaving the tutorial stopped at ⏳ Link Devices to Animal entities with no error shown.

⭐ Verified intermittent rather than assumed: the identical payload against the same agent gave exit=52 then exit=0 back to back. A single device is accepted with 201 throughout, and 31 KB is nowhere near the agent's 1 MB expressLimit, so it isn't a size limit.

--retry 10 --retry-all-errors --retry-delay 10 on those two calls; tested end-to-end, after which the tutorial starts cleanly (services exits 0).

Found while running all sixteen NGSI-LD tutorials against a different NGSI-LD broker — this was one of four that could never be started.