Bug 1771693

Description of problem:
Per the customer:

"We use the API to manage our host groups, and are finding the new option 'Deploy On' is not being returned by the RESTAPI when performing a CURL against a given host group with the setting."

Version-Release number of selected component (if applicable):
N/A

How reproducible:
100%

Steps to Reproduce:
1. create a new host group (with or without an entry in 'deployed on')
2. call the API to display the host group's JSON output
3.

Actual results:
There is not a listing for 'Deployed On' (either 'NULL' or what was chosen)

Expected results:
A parameter listing either NULL or the entry for 'Deployed On'

Additional info:
Sample output from my test 6.5 Satellite on latest 6.5:

# curl -k -u admin https://oblivion.usersys.redhat.com/api/v2/hostgroups/?search=test | json_reformat
Enter host password for user 'admin':
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  1363    0  1363    0     0   2574      0 --:--:-- --:--:-- --:--:--  2576
{
    "total": 1,
    "subtotal": 1,
    "page": 1,
    "per_page": 20,
    "search": "test",
    "sort": {
        "by": null,
        "order": null
    },
    "results": [
        {
            "subnet_id": null,
            "subnet_name": null,
            "operatingsystem_id": 4,
            "operatingsystem_name": "RedHat 7.7",
            "domain_id": null,
            "domain_name": null,
            "environment_id": 2,
            "environment_name": "common",
            "compute_profile_id": null,
            "compute_profile_name": null,
            "ancestry": null,
            "parent_id": null,
            "parent_name": null,
            "ptable_id": 99,
            "ptable_name": "Kickstart default",
            "medium_id": null,
            "medium_name": null,
            "pxe_loader": "PXELinux BIOS",
            "subnet6_id": null,
            "subnet6_name": null,
            "architecture_id": 1,
            "architecture_name": "x86_64",
            "realm_id": null,
            "realm_name": null,
            "created_at": "2019-11-12 18:28:58 UTC",
            "updated_at": "2019-11-12 18:28:58 UTC",
            "id": 1,
            "name": "test",
            "title": "test",
            "description": "test",
            "puppet_proxy_id": 1,
            "puppet_proxy_name": "oblivion.usersys.redhat.com",
            "puppet_ca_proxy_id": 1,
            "puppet_ca_proxy_name": "oblivion.usersys.redhat.com",
            "openscap_proxy_id": 1,
            "openscap_proxy_name": "oblivion.usersys.redhat.com",
            "puppet_proxy": {
                "name": "oblivion.usersys.redhat.com",
                "id": 1,
                "url": "https://oblivion.usersys.redhat.com:9090"
            },
            "puppet_ca_proxy": {
                "name": "oblivion.usersys.redhat.com",
                "id": 1,
                "url": "https://oblivion.usersys.redhat.com:9090"
            },
            "openscap_proxy": {
                "name": "oblivion.usersys.redhat.com",
                "id": 1,
                "url": "https://oblivion.usersys.redhat.com:9090"
            }
        }
    ]
}