Still no dice for me.  Weird.

Here is the cloud-config - copied directly from https://docs.openstack.org/devstack/latest/guides/single-vm.html this time, even without replacing the password "password".

    $ cat > devstack-userdata.yaml                                                                                                                                                
    #cloud-config
    
    users:
      - default
      - name: stack
        lock_passwd: False
        sudo: ["ALL=(ALL) NOPASSWD:ALL\nDefaults:stack !requiretty"]
        shell: /bin/bash
    
    write_files:
      - content: |
            #!/bin/sh
            DEBIAN_FRONTEND=noninteractive sudo apt-get -qqy update || sudo yum update -qy
            DEBIAN_FRONTEND=noninteractive sudo apt-get install -qqy git || sudo yum install -qy git
            sudo chown stack:stack /home/stack
            cd /home/stack
            git clone https://git.openstack.org/openstack-dev/devstack
            cd devstack
            echo '[[local|localrc]]' > local.conf
            echo ADMIN_PASSWORD=password >> local.conf
            echo DATABASE_PASSWORD=password >> local.conf
            echo RABBIT_PASSWORD=password >> local.conf
            echo SERVICE_PASSWORD=password >> local.conf
            ./stack.sh
        path: /home/stack/start.sh
        permissions: 0755
    
    runcmd:
      - su -l stack ./start.sh

Here is how I launched the VM:
    
    $ openstack server create --os-cloud=ms1-test  --image ubuntu16.04 --flavor large --key-name someprivatekey --nic net-id=3d2ec639-098b-47f8-896c-bc67cf321a2b --user-data=devstack-userdata.yaml devstackubuntu --availability-zone osl3
    +-----------------------------+------------------------------------------------------------------+
    | Field                       | Value                                                            |
    +-----------------------------+------------------------------------------------------------------+
    | OS-DCF:diskConfig           | MANUAL                                                           |
    | OS-EXT-AZ:availability_zone | osl3                                                             |
    | OS-EXT-STS:power_state      | NOSTATE                                                          |
    | OS-EXT-STS:task_state       | scheduling                                                       |
    | OS-EXT-STS:vm_state         | building                                                         |
    | OS-SRV-USG:launched_at      | None                                                             |
    | OS-SRV-USG:terminated_at    | None                                                             |
    | accessIPv4                  |                                                                  |
    | accessIPv6                  |                                                                  |
    | addresses                   |                                                                  |
    | adminPass                   | aB6ZSw6hWa9T                                                     |
    | config_drive                |                                                                  |
    | created                     | 2018-03-19T13:17:08Z                                             |
    | flavor                      | large (09003000)                                                 |
    | hostId                      |                                                                  |
    | id                          | 63eb7cfa-acf4-4b09-b9c3-e09af5fb1c9e                             |
    | image                       | ubuntu16.04 (27f79cf0-5b3d-4dea-9e67-45d98ee92c36)               |
    | key_name                    | someprivatekey                                                   |
    | name                        | devstackubuntu                                                   |
    | progress                    | 0                                                                |
    | project_id                  | 2b633b0b2ca84e748e37b0b12bbb81fc                                 |
    | properties                  |                                                                  |
    | security_groups             | name='default'                                                   |
    | status                      | BUILD                                                            |
    | updated                     | 2018-03-19T13:17:09Z                                             |
    | user_id                     | f0a681996f5c6b1b423cfa5da75bb534f2a9ef29dce4a96c9e8b9d1de630c3b4 |
    | volumes_attached            |                                                                  |
    +-----------------------------+------------------------------------------------------------------+

I will attach the log shortly.