Make product deletes more clear in logging

The log shows information like this when a product is processed, whether it is deleted or not:

INFO thread=31 [indexer] indexed product id=urn:usgs-product:ci:moment-tensor:ci37295831_mt1:1452791153510 EVENT_UPDATED ci37295831 => ci37295831

Listeners can check the product status, but the log (at least) should be more explicit that the indexed product was a delete.