Cloned from https://bugzilla.redhat.com/show_bug.cgi?id=1339172

Description of problem:
Impossible to change default value 'thin' for new volumes in Vmware compute profile

How reproducible:
Always

Steps to Reproduce:
1. Check that 'thin' value is set to false for new_volumes section:

$ curl -s -X GET -H "Authorization: Basic xxxxxxxxxxxxxx" -H "Accept:application/json" -H "Content-Type: application/json" https://foreman.example.com.com/api/v2/compute_profiles/4|python -mjson.tool
{
    "compute_attributes": [
        {
            "id": 1,
# ...
            "vm_attrs": {

                "volumes_attributes": {
                    "0": {
                        "_delete": "",
                        "datastore": "my-store-1",
                        "eager_zero": "false",
                        "name": "Hard disk",
                        "size_gb": "50",
                        "thin": "false" 
                    },
                    "new_volumes": {
                        "_delete": "",
                        "datastore": "my-store-1",
                        "eager_zero": "false",
                        "name": "Hard disk",
                        "size_gb": "10",
                        "thin": "true"  <----------
                    }
                }
            }
        }
    ],
2. Update 'thin' field:

curl -s -X PUT -H "Authorization: Basic xxxxxxxxxxxxxxx" -H "Accept:application/json" -H "Content-Type: application/json" https://foreman.example.com/api/v2/compute_resources/1 -d '{"compute_attributes":[{"id":1,"name":"1CPUsand2048MBmemory","compute_resource_id":1,"compute_resource_name":"my-resource","compute_profile_id":4,"compute_profile_name":"my-profile","vm_attrs":{"volumes_attributes":{"new_volumes":{"datastore":"my-store-1","name":"Harddisk","size_gb":"30",

"thin":"false",  <-----

"eager_zero":"false","_delete":""}}}}]}'

Actual results:
"thin" is still "true" 

Expected results:
"thin" should be changed to "false"