overit_network fails when trying to create a network that uses an external provider.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
module ovirt_network


##### ANSIBLE VERSION
```
ansible 2.9.1
  config file = /Users/krist/Work/INFRA/Bern/PlopslandRHEV/ansible.cfg
  configured module search path = ['/Users/krist/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/local/Cellar/ansible/2.9.1/libexec/lib/python3.7/site-packages/ansible
  executable location = /usr/local/bin/ansible
  python version = 3.7.5 (default, Nov  1 2019, 02:16:23) [Clang 11.0.0 (clang-1100.0.33.8)]##### CONFIGURATION
```
##### OS / ENVIRONMENT

MacOSX 10.15

##### STEPS TO REPRODUCE
Consider the following playbook:

```
- name: prepare the RHEV cluster 
  hosts: localhost


  tasks:

  - block:
      - name: Obtain SSO Token
        ovirt_auth:
          url: "{{ ovirt_api }}"
          username: admin@internal
          ca_file: files/ca.pem
          password: "{{ ovirt_password }}"
    
      - name: Create private networks
        ovirt_network:
          auth: "{{ ovirt_auth }}"
          data_center: Default
          name: boot
          vm_network: true
          external_provider: ovirt-provider-ovn
          state: present

    always:
      - name: Always revoke the SSO token
        ovirt_auth:
          state: absent
          ovirt_auth: "{{ ovirt_auth }}"
```

##### EXPECTED RESULTS

A network "boot" is created, using the external provider ovirt-provider-ovn

##### ACTUAL RESULTS

An error is thrown: 

```
TASK [Create private networks] *********************************************************************************************************
An exception occurred during task execution. To see the full traceback, use -vvv. The error was: Exception: Entity 'boot' was not found.
fatal: [localhost]: FAILED! => {"changed": false, "msg": "Entity 'boot' was not found."}
```

Looking at hte source it appears then when you define a external provider that was is in fact attempted is to import a network form that external provider, not crearte one:

```
  if module.params.get('external_provider'):
                ret = networks_module.import_external_network()
            else:
                ret = networks_module.create(search_params=search_params)
```

That is not what you would expect, not according to the docs anyway.


def import_external_network(self):
        ons_service = self._connection.system_service().openstack_network_providers_service()
        on_service = ons_service.provider_service(get_id_by_name(ons_service, self.param('external_provider')))
        networks_service = on_service.networks_service()
        network_service = networks_service.network_service(get_id_by_name(networks_service, self.param('name')))
        network_service.import_(data_center=otypes.DataCenter(name=self._module.params['data_center']))
        return {"network": get_dict_of_struct(network_service.get()), "changed": True}
    def build_entity(self):
        return otypes.Network(
            name=self._module.params['name'],
            comment=self._module.params['comment'],
            description=self._module.params['description'],
            id=self._module.params['id'],
            data_center=otypes.DataCenter(
                name=self._module.params['data_center'],
            ) if self._module.params['data_center'] else None,
            vlan=otypes.Vlan(
                self._module.params['vlan_tag'],
            ) if self._module.params['vlan_tag'] else None,
            usages=[
                otypes.NetworkUsage.VM if self._module.params['vm_network'] else None
            ] if self._module.params['vm_network'] is not None else None,
            mtu=self._module.params['mtu'],
        )
    def post_create(self, entity):