Comment 0 for bug 1933763

Kolla Ansible version: Train
Distro: CentOS 7

run host bootstrap
run prechecks
and get:

TASK [prechecks : Checking docker SDK version] *********************************
fatal: [primary]: FAILED! => {
    "changed": false,
    "cmd": [
        "/usr/bin/python2",
        "-c",
        "import docker; print(docker.__version__)"
    ],
    "delta": "0:00:00.154198",
    "end": "2021-06-27 15:36:06.905852",
    "failed_when_result": true,
    "invocation": {
        "module_args": {
            "_raw_params": "/usr/bin/python2 -c \"import docker; print(docker.__version__)\"",
            "_uses_shell": false,
            "argv": null,
            "chdir": null,
            "creates": null,
            "executable": null,
            "removes": null,
            "stdin": null,
            "warn": true
        }
    },
    "msg": "non-zero return code",
    "rc": 1,
    "start": "2021-06-27 15:36:06.751654",
    "stderr": "Traceback (most recent call last):\n File \"<string>\", line 1, in <module>\n File \"/usr/lib/python2.7/site-packages/docker/__init__.py\", line 2, in <module>\n from .api import APIClient\n File \"/usr/lib/python2.7/site-packages/docker/api/__init__.py\", line 2, in <module>\n from .client import APIClient\n File \"/usr/lib/python2.7/site-packages/docker/api/client.py\", line 8, in <module>\n import websocket\n File \"/usr/lib/python2.7/site-packages/websocket/__init__.py\", line 22, in <module>\n from ._app import WebSocketApp\n File \"/usr/lib/python2.7/site-packages/websocket/_app.py\", line 25, in <module>\n import selectors\nImportError: No module named selectors",
    "stderr_lines": [
        "Traceback (most recent call last):",
        " File \"<string>\", line 1, in <module>",
        " File \"/usr/lib/python2.7/site-packages/docker/__init__.py\", line 2, in <module>",
        " from .api import APIClient",
        " File \"/usr/lib/python2.7/site-packages/docker/api/__init__.py\", line 2, in <module>",
        " from .client import APIClient",
        " File \"/usr/lib/python2.7/site-packages/docker/api/client.py\", line 8, in <module>",
        " import websocket",
        " File \"/usr/lib/python2.7/site-packages/websocket/__init__.py\", line 22, in <module>",
        " from ._app import WebSocketApp",
        " File \"/usr/lib/python2.7/site-packages/websocket/_app.py\", line 25, in <module>",
        " import selectors",
        "ImportError: No module named selectors"
    ],
    "stdout": "",
    "stdout_lines": []
}

The reason is pip on CentOS 7 is too old to choose py2-compatible versions of docker sdk deps.