Auth: reuse existing token, when scope parameters are not defined

[kayrus]

Expected Behavior

Terraform OpenStack provider should reuse an existing token, when no scope is defined. This will resolve issues, when token is issued from application credentials and it is not allowed to create its subtoken.

Actual Behavior

Terraform OpenStack provider issues a new scoped token for every auth request, which contains the existing OS_AUTH_TOKEN.

References

gophercloud/gophercloud#1566
https://github.com/terraform-providers/terraform-provider-openstack/pull/861#issuecomment-531261745