Follow up for #21039.
We can revert the previous change and do that a bit smarter than it was.
Patch tested successfully manually on ec2 with 2 nodes with a configuration like:
```yml
discovery.type: ec2
network.host: ["_local_", "_site_", "_ec2_"]
cloud.aws.region: us-west-2
```
(cherry picked from commit fbbeded)
Backport of #21048 in master branch
e5d9f393f1