Description of problem:
When starting a migration it fails as the request is denied. And the request is denied because no conversion host is associated to the destination  ext_management_system. Below is an example of the failing relationship:

```
irb(main):029:0> ConversionHost.first.ext_management_system.conversion_hosts
  ConversionHost Load (0.3ms)  SELECT  "conversion_hosts".* FROM "conversion_hosts" ORDER BY "conversion_hosts"."id" ASC LIMIT $1  [["LIMIT", 1]]
  ConversionHost Inst Including Associations (0.1ms - 1rows)
  ManageIQ::Providers::Openstack::CloudManager::Vm Load (0.5ms)  SELECT  "vms".* FROM "vms" WHERE "vms"."template" = $1 AND "vms"."type" IN ('ManageIQ::Providers::Openstack::CloudManager::Vm') AND "vms"."id" = $2 LIMIT $3  [["template", "f"], ["id", 162], ["LIMIT", 1]]
  ManageIQ::Providers::Openstack::CloudManager::Vm Inst Including Associations (0.3ms - 1rows)
  ExtManagementSystem Load (0.3ms)  SELECT  "ext_management_systems".* FROM "ext_management_systems" WHERE "ext_management_systems"."id" = $1 LIMIT $2  [["id", 6], ["LIMIT", 1]]
  ExtManagementSystem Inst Including Associations (0.3ms - 1rows)
  ConversionHost Load (0.4ms)  SELECT "conversion_hosts".* FROM "conversion_hosts" INNER JOIN "hosts" ON "conversion_hosts"."resource_id" = "hosts"."id" WHERE "hosts"."ems_id" = $1 AND "conversion_hosts"."resource_type" = $2  [["ems_id", 6], ["resource_type", "Host"]]
  ConversionHost Inst Including Associations (0.0ms - 0rows)
  ConversionHost Load (0.6ms)  SELECT "conversion_hosts".* FROM "conversion_hosts" INNER JOIN "vms" ON "conversion_hosts"."resource_id" = "vms"."id" WHERE "vms"."type" IN ('Vm', 'ManageIQ::Providers::CloudManager::Vm', 'ManageIQ::Providers::InfraManager::Vm', 'VmServer', 'ManageIQ::Providers::Amazon::CloudManager::Vm', 'ManageIQ::Providers::Azure::CloudManager::Vm', 'ManageIQ::Providers::Google::CloudManager::Vm', 'ManageIQ::Providers::Openstack::CloudManager::Vm', 'ManageIQ::Providers::Vmware::CloudManager::Vm', 'VmXen', 'ManageIQ::Providers::Kubevirt::InfraManager::Vm', 'ManageIQ::Providers::Redhat::InfraManager::Vm', 'ManageIQ::Providers::Microsoft::InfraManager::Vm', 'ManageIQ::Providers::Vmware::InfraManager::Vm') AND "vms"."template" = $1 AND "vms"."ems_id" = $2 AND "conversion_hosts"."resource_type" = $3  [["template", "f"], ["ems_id", 6], ["resource_type", "VmOrTemplate"]]
  ConversionHost Inst Including Associations (0.0ms - 0rows)
=> []
```

Actually, the conversion_hosts table contains `ManageIQ::Providers::Openstack::CloudManager::Vm` for the resource type of the existing conversion host.

The impact is that no migration will work.


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


How reproducible: 100%


Steps to Reproduce:
1. Create a conversion host from API:

curl -sk -u admin:smartvm http://localhost:3000/api/conversion_hosts -X POST -d '{"action": "create", "resource": {"resource_type": "ManageIQ::Providers::Openstack::CloudManager::Vm", "resource_id": 162, "vmware_vddk_package_url": "http://file.example.com/vddk/VMware-vix-disklib-stable.tar.gz", "conversion_host_ssh_private_key": "-----BEGIN RSA PRIVATE KEY-----\nMIIE...", "address": "192.168.0.10"}}'

2. Try to list the conversion host of the provider

irb> ConversionHost.first.ext_management_system.conversion_hosts


Actual results: returns an empty array


Expected results: returns the created conversion host