Description of problem:
When a vm interface is being attached to an external network, engine should provide the custom properties as defined on the nic's profile.

However, due to internal implementation, the network devices as configured on the vm, failed to be identified at run-time.

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


How reproducible:
always

Steps to Reproduce:
1. Add external network EXNET
2. Assing the vnic profile EXNET to a vm.
3. Start the VM

Actual results:
No custom properties are provided to vdsm 'create' vm verb, hence vm failed to start.

Expected results:
The custom element should contain the external provider and its network details, i.e.:

'custom': {'plugin_type': 'OPEN_VSWITCH', 'security_groups': 'd37cd9aa-6eed-4bdc-b4c4-31b5aecf6048', 'vnic_id': 'f2572c9d-c9e9-44ba-9ebe-7be383aeb2f1', 'provider_type': 'OPENSTACK_NETWORK'}

Additional info: