fix 645: set tags in resourceNetboxTenantRead

[sempervictus]

address #645

[sempervictus]

These tests are ... "illogical":

=== NAME  TestAccNetboxTenant_tags
    resource_netbox_tenant_test.go:81: Step 1/3 error: After applying this test step and performing a `terraform refresh`, the plan was not empty.
        stdout
        
        
        Terraform used the selected providers to generate the following execution
        plan. Resource actions are indicated with the following symbols:
          ~ update in-place
        
        Terraform will perform the following actions:
        
          # netbox_tenant.test_tags will be updated in-place
          ~ resource "netbox_tenant" "test_tags" {
                id          = "69"
                name        = "test-tenant_tags-gjusrf4zcd"
              ~ tags        = [
                  + "test-tenant_tags-gjusrf4zcda",
                ]
                # (2 unchanged attributes hidden)
            }
        
        Plan: 0 to add, 1 to change, 0 to destroy.
--- FAIL: TestAccNetboxTenant_tags (1.88s)

is exactly what should be happening because the provider ignored the need to populate its own fields and really the tests should always fail on any data field being null since a read of an empty type would still produce that type, just with no data in it.