Does not seem to working with Custom network

[rajeshkumarkt]

Using custom network requires the subnetwork to be specified as part of the create instance command. It does not look like we the command accepts a subnetwork

To reproduce

1. Create a Custom network and subnetwork in GCP
2. Use the custom network while running the bdutil.
3. Log messages says that it requires a subnetwork
   Could not find any way to specify a subnetwork

Logs:
`

******************* gcloud compute stdout *******************

******************* gcloud compute stderr *******************
ERROR: (gcloud.compute.instances.create) Some requests did not succeed:

• Invalid value for field 'resource.networkInterfaces[0]': ''. Subnetwork should be specified for custom subnetmode network

************ ERROR logs from gcloud compute stderr ************
ERROR: (gcloud.compute.instances.create) Some requests did not succeed:
`

[usopan]

Facing same issue . Any resolution for this?

[leandrosouza]

same problem.