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##### SUMMARY
<!--- Explain the problem briefly below -->
`ansible-inventory` is supposed to return JSON...
but it does not when installing anisble@devel, and running a GCE inventory update with this `gcp_compute.yml` to use the gcp inventory plugin:

```
auth_kind: serviceaccount
filters: null
plugin: gcp_compute
projects:
- myproject
service_account_file: creds.json
```

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
<!--- Write the short name of the module, plugin, task or feature below, use your best guess if unsure -->
gcp inventory plugin
##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```paste below
 ansible-inventory --version    
ansible-inventory 2.9.0.dev0
  config file = /etc/ansible/ansible.cfg
  configured module search path = ['/home/elijah/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /home/elijah/venvs/py36towerqa/lib64/python3.6/site-packages/ansible 
  executable location = /home/elijah/venvs/py36towerqa/bin/ansible-inventory                            
  python version = 3.6.8 (default, Feb 19 2019, 21:10:40) [GCC 9.0.1 20190209 (Red Hat 9.0.1-0.4)] 
```

##### CONFIGURATION
<!--- Paste verbatim output from "ansible-config dump --only-changed" between quotes -->
```paste below
#no output
```

##### OS / ENVIRONMENT
<!--- Provide all relevant information below, e.g. target OS versions, network device firmware, etc. -->


##### STEPS TO REPRODUCE
<!--- Describe exactly how to reproduce the problem, using a minimal test-case -->
1) Create gcp_comput.yml and creds.json to access your gcp account
2) Create python36 venv
3) install anisble@stable-2.8
4) run `ansible-inventory -i gcp_compute.yml --list > ouput.28`
5) Inspect the output, see that it is valid JSON.
6) install ansible@devel
4) run `ansible-inventory -i gcp_compute.yml --list > ouput.devel`
7) Inspect output, see that before the part that starts the JSON that looks like:
```
{
    "_meta": {
        "hostvars": {
```
there is a bug chunk of key/value pairs in a list:
```
[{'key': 'blahkey', 'value': 'blahvalue}, {'key': 'ssh-keys', 'value': 'somebody's key'} {'key': 'more keys', 'value': 'more values' ...... ] 
```


<!--- HINT: You can paste gist.github.com links for larger files -->

##### EXPECTED RESULTS
<!--- Describe what you expected to happen when running the steps above -->
JSON

##### ACTUAL RESULTS
<!--- Describe what actually happened. If possible run with extra verbosity (-vvvv) -->
List of key/value pairs then regular json ouput
<!--- Paste verbatim command output between quotes -->
```paste below

```
This is a tower blocker for the next release of ansible.
 (private repo) https://github.com/ansible/tower/issues/3605

use_contrib_script_compatible_sanitization:
          description:
            - By default this plugin is using a general group name sanitization to create safe and usable group names for use in Ansible.
              This option allows you to override that, in efforts to allow migration from the old inventory script.
            - For this to work you should also turn off the TRANSFORM_INVALID_GROUP_CHARS setting,
              otherwise the core engine will just use the standard sanitization on top.
            - This is not the default as such names break certain functionality as not all characters are valid Python identifiers
              which group names end up being used as.
          type: bool
          default: False
          version_added: '2.8'
        retrieve_image_info:
          description:
            - Populate the C(image) host fact for the instances returned with the GCP image name
            - By default this plugin does not attempt to resolve the boot image of an instance to the image name cataloged in GCP
              because of the performance overhead of the task.
            - Unless this option is enabled, the C(image) host variable will be C(null)
          type: bool
          default: False
          version_added: '2.8'
'''
EXAMPLES = '''
plugin: gcp_compute
zones: # populate inventory with instances in these regions
  - us-east1-a
projects:
  - gcp-prod-gke-100
  - gcp-cicd-101
filters:
  - machineType = n1-standard-1