Add importing of resources

[amhn]

Summary

Add import functions to resources to allow importing of resources defined in netbox.

Example

Usage

$ terraform import netbox_ip_addresses.ip_test 1

Use this to import the address with ID 1 into the terraform state.

Implementation

See amhn@9b13e59 for possible implementation.
Tested with terraform 0.14.8 and 0.13.6 and netbox 3e4c35ffd9f6 (v2.10.6)

Tested ressources:

• ipam_aggreagate
• ipam_ip_addresses
• ipam_prefix
• ipam_service
• ipam_vlan
• ipam_vlan_group
• virtualization_interface
• virtualization_vm

Not tested:

• tenancy_tenant
• tenancy_tenant_group

[smutel]

Hello. Could you please open a PR ? Thanks.