Fixes#8612
The SSL Policy is optional - if you don't add it and create a HTTPS Alb
Listener, AWS will add the policy for you. Without being computed, we
would get a diff
```
% make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSALBListener_'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
2016/09/02 17:16:33 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSALBListener_
-timeout 120m
=== RUN TestAccAWSALBListener_basic
--- PASS: TestAccAWSALBListener_basic (70.45s)
=== RUN TestAccAWSALBListener_https
--- PASS: TestAccAWSALBListener_https (63.20s)
PASS
ok github.com/hashicorp/terraform/builtin/providers/aws 133.667s
```
stack72