[elasticsearch] use bash to run scripts

[ebuildy]

To simplify a bit

• Chart version not bumped (the versions are all bumped and released at the same time)
• README.md updated with any new values or changes
• Updated template tests in ${CHART}/tests/*.py
• Updated integration tests in ${CHART}/examples/*/test/goss.yaml

[elasticmachine]

Since this is a community submitted pull request, a Jenkins build has not been kicked off automatically. Can an Elastic organization member please verify the contents of this patch and then kick off a build manually?

[JorisAndrade]

This also fix a bug in 7.16.0 where the readiness is not working

  Warning  Unhealthy  3m2s (x44 over 10m)  kubelet  Readiness probe failed: Elasticsearch is already running, lets check the node is healthy
curl --output /dev/null -k -XGET -s -w '%{http_code}' ${BASIC_AUTH} http://127.0.0.1:9200/ failed with HTTP code 200
sh: 30: [[: not found
sh: 35: [[: not found
sh: 37: [[: not found

[ebuildy]

Yes , this is why I have created this PR, didnt investigate it why is no more working. Tests are runing fine, I am doing the PR.

[jmlrt]

Thanks for this PR @ebuildy, this was fixed in #1458 + #1464 + #1466.
I should have looked at your PR before fixing it in a hurry, your's was a lot cleaner ^^.