Update example product to use stemcell_selector property type
Update example product to use stemcell_selector property type

[#164618389] Tile authors can upload tiles that support multiple stemcells (and get/put in API)

Signed-off-by: Nick Webb <7fba9782dbb7ee0d42d2994cde65927fd056c6b7@pivotal.io>

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