failing to ssh into a FreeBSD AMI post packer build

_This issue was originally opened by @david-peters-aitch2o as hashicorp/packer#10854. 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._

---

#### Overview of the Issue

with an extremely simple build, booting the ec2-instance it will fail to ssh in

#### Reproduction Steps

build with the following file:
```json
{
"variables": {
"DB_USERNAME": "{{env `DB_USERNAME`}}",
"DB_PASSWORD": "{{env `DB_PASSWORD`}}"
},
"builders": [{
"type": "amazon-ebs",
"region": "ap-southeast-2",
"profile": "test-workspace-dev",
"source_ami": "ami-0e0a9bebd811801a4",
"instance_type": "t2.medium",
"ssh_username": "ec2-user",
"ami_name": "instance {{timestamp}}",
"ssh_timeout": "15m",
"user_data_file": "user_data.txt"
}]
}
}
```

user_data.txt file contains

```shell
#!/bin/sh
env ASSUME_ALWAYS_YES=YES pkg install sudo python bash bash-completion
```

deploy from above AMI and trying to ssh in with your keys will fail, deploy from the ami-0e0a9bebd811801a4 AMI, ssh with your keys and it works

### Packer version
[INFO] Packer version: 1.7.0 [go1.15.8 linux amd64]

### Simplified Packer Buildfile

see above

### Operating system and Environment details

OS is FreeBSD 12
base AMI is ami-0e0a9bebd811801a4

### Log Fragments and crash.log files

logs are fine as it builds as expected