packer ssh private repo failing

build.log

1528837782,,ui,message,    amazon-ebs: Processing triggers for libc-bin (2.23-0ubuntu10) ...
1528837782,,ui,message,    amazon-ebs: Processing triggers for systemd (229-4ubuntu21.2) ...
1528837782,,ui,message,    amazon-ebs: Processing triggers for ureadahead (0.100.0-19) ...
1528837782,,ui,message,    amazon-ebs: Processing triggers for ufw (0.35-0ubuntu2) ...
1528837783,,ui,message,    amazon-ebs: # github.com:22 SSH-2.0-libssh_0.7.0
1528837783,,ui,message,    amazon-ebs: # github.com:22 SSH-2.0-libssh_0.7.0
1528837783,,ui,message,    amazon-ebs: # github.com:22 SSH-2.0-libssh_0.7.0
1528837783,,ui,message,    amazon-ebs: Cloning into '/app'...
1528837783,,ui,message,    amazon-ebs: Host key verification failed.
1528837783,,ui,message,    amazon-ebs: fatal: Could not read from remote repository.
1528837783,,ui,message,    amazon-ebs:
1528837783,,ui,message,    amazon-ebs: Please make sure you have the correct access rights
1528837783,,ui,message,    amazon-ebs: and the repository exists.
1528837783,,ui,say,==> amazon-ebs: Terminating the source AWS instance...
1528837843,,ui,say,==> amazon-ebs: Cleaning up any extra volumes...
1528837844,,ui,say,==> amazon-ebs: No volumes to clean up%!(PACKER_COMMA) skipping
1528837844,,ui,say,==> amazon-ebs: Deleting temporary security group...
1528837844,,ui,say,==> amazon-ebs: Deleting temporary keypair...
1528837844,,ui,error,Build 'amazon-ebs' errored: Script exited with non-zero exit status: 128
1528837844,,error-count,1
1528837844,,ui,error,\n==> Some builds didn't complete successfully and had errors:
1528837844,amazon-ebs,error,Script exited with non-zero exit status: 128
1528837844,,ui,error,--> amazon-ebs: Script exited with non-zero exit status: 128
1528837844,,ui,say,\n==> Builds finished but no artifacts were created.

packer-client.json

{
  "variables": {
    "aws_access_key": "",
    "aws_secret_key": "",
    "region": "us-east-1",
    "instance_type": "t2.micro"
  },
  "builders": [{
    "type": "amazon-ebs",
    "access_key": "{{user `aws_access_key`}}",
    "secret_key": "{{user `aws_secret_key`}}",
    "region": "{{user `region`}}",
    "instance_type": "{{user `instance_type`}}",
    "ssh_username": "ubuntu",
    "ami_name": "packer-client {{timestamp}}",
    "source_ami_filter": {
      "filters": {
        "virtualization-type": "hvm",
        "name": "ubuntu/images/hvm-ssd/ubuntu-xenial-16.04-amd64-server-*",
        "root-device-type": "ebs"
      },
      "owners": ["099720109477"],
      "most_recent": true
    }
  }],
  "provisioners": [{
    "type": "shell",
    "scripts": [ "scripts/packer_install_client_softwares.sh", "scripts/deploy.sh"],
    "execute_command": "{{ .Vars }} sudo -E sh '{{ .Path }}'",
    "pause_before": "10s"
  }]
}