Un-skip Metricbeat kibana module flaky tests

[ycombinator]

Resolves #11261.

This PR:

• un-skips the currently-skipped flaky integration tests for the Metricbeat kibana module
• makes the Kibana docker health check more robust, similar to the one in

  beats/x-pack/libbeat/docker-compose.yml

  Lines 49 to 53 in e2b1084

  	healthcheck:
  	test: ["CMD-SHELL", 'python -c ''import urllib, json; response = urllib.urlopen("http://myelastic:changeme@localhost:5601/api/status"); data = json.loads(response.read()); exit(1) if data["status"]["overall"]["state"] != "green" else exit(0);''']
  	retries: 1200
  	interval: 5s
  	start_period: 60s

[ycombinator]

jenkins, test this

[ruflin]

jenkins, test this