EC2 SSH Timeout Flakiness

_This issue was originally opened by @njgrisafi as hashicorp/packer#10992. It was migrated here as a result of the [Packer plugin split](https://github.com/hashicorp/packer/issues/8610#issuecomment-770034737). The original body of the issue is below._

- Packer Version: `1.7.0`
- Host platform: `macOS BigSur 11.3`
- Debug log output from [PACKER_LOG=1 packer build cmd](https://gist.github.com/njgrisafi/fbc86b1a80df96a69891713cde6c6092#file-packer-logs-txt)

I'm using packer to automate the creation of AWS AMIs. Using packer locally has been a bit frustrating due to frequent SSH timeout errors. My work around is to retry the `packer build` command until ssh connects successfully.

This happens for any packer buildfile that requires SSH via EC2. The EC2 instance is ready and available but packer says it can't connect. I've ran packer in debug mode and confirmed I can connect to the EC2 via SSH when packer says it got a timeout.

I'm thinking this could be an issue with my host machine but not sure. Any help is appreciated!