provider/openstack: openstack router admin state
provider/openstack: openstack router admin state

Change openstack router resource admin state from a string to a
boolean.

Same technique as mitchellh's fix in
https://github.com/hashicorp/terraform/pull/1745

haxorof/terraform-provider-openstack,haxorof/terraform-provider-openstack,haxorof/terraform-provider-openstack