Action packs.uninstall does not return valid JSON

SUMMARY

Running st2 run packs.uninstall packs=examples -j does not return well-formed JSON data.

ISSUE TYPE

Bug Report

STACKSTORM VERSION

Paste the output of st2 --version:

st2 3.0dev (2f5fa9b), on Python 2.7.12

OS / ENVIRONMENT / INSTALL METHOD

Installed on Ubuntu 16.04 with st2vagrant.

STEPS TO REPRODUCE

1. Fire up Ubuntu 16.04 VM with st2vagrant.
2. Run:

   # sudo cp -r /usr/share/doc/st2/examples/ /opt/stackstorm/packs/
   # st2 run packs.setup_virtualenv packs=examples -j
   # sudo st2ctl reload --register-all
   # st2 run packs.uninstall packs=examples -j
   

EXPECTED RESULTS

Valid JSON.

ACTUAL RESULTS

Invalid JSON:

{
    "action": {
        "ref": "packs.uninstall"
    },
    "end_timestamp": "2019-04-18T02:52:47.720613Z",
    "id": "5cb7e67ca08f813f457b8a25",
    "parameters": {
        "packs": [
            "examples"
        ]
    },
    "result": {
        "exit_code": 0,
        "result": null,
        "stderr": "st2.actions.python.UninstallPackAction: DEBUG    Deleting pack directory \"/opt/stackstorm/packs/examples\"\nst2.actions.python.UninstallPackAction: DEBUG    Deleting virtualenv \"/opt/stackstorm/virtualenvs/examples\" for pack \"examples\"\n",
        "stdout": ""
    },
    "result_task": "delete packs",
    "start_timestamp": "2019-04-18T02:52:44.274245Z",
    "status": "succeeded"
}
[
    {
        "action": "packs.unload",
        "id": "5cb7e67ca08f813fa9f006a3",
        "start_timestamp": "2019-04-18T02:52:44.527055Z",
        "status": "succeeded (1s elapsed)",
        "task": "unregister packs"
    },
    {
        "action": "packs.delete",
        "id": "5cb7e67ea08f813fa9f006a5",
        "start_timestamp": "2019-04-18T02:52:46.645818Z",
        "status": "succeeded (1s elapsed)",
        "task": "delete packs"
    }
]

The object and the array are both well-formed JSON, but simply concatenating them together does not constitute result in valid JSON.

Reproduce the issue with st2 run packs.uninstall packs=examples -j and inspect the CLI handling for the packs.uninstall action. Trace how the displayed object and task-status array are serialized, then verify that the command emits one valid JSON document instead of concatenated JSON values.