update example product to have a second stemcell selector
update example product to have a second stemcell selector

- this one has a default

[#165072612] When the value of a stemcell selector has a default, the stemcell should be automatically bound to the highest patch release (if present) when the product is added

pivotal-cf-experimental/ops-manager-example,pivotal-cf-experimental/ops-manager-example,pivotal-cf-experimental/ops-manager-example,pivotal-cf-experimental/ops-manager-example