A common scenario in the API is to get a sigle value from a distributed
object that has a get_stats method.
The helper function would get the object and a function that return a
single value from the stat object and would perform the map_reduce.
It would return a future that can be used as a return value from the
API.
Signed-off-by: Amnon Heiman <amnon@cloudius-systems.com>