Create php_mongo_collection_find to cover both RP copying and cursor creation.
MONGO_METHOD(MongoCollection, find, …) -> php_mongo_collection_find().
Convert MONGO_METHOD in mongo_db_list_collections_legacy to real cursor C functions.

MONGO_METHOD -=5
PHP-1225: Implement command version of listCollections.
Make sure to bail out as soon as we can with a descriptive exception.
Added test cases for command listCollections, and make sure we only force primary when we are in a replica set.
Added other replicaset related test cases.