Implement a more accurate failure response to data points write

[mohabusama]

Data points are written in async way that could lead to falsely show write operation failed to the caller.

Example:

[Caller] ----put data points with timeout=5s---> [KairosDB]----data_points_insert takes 10s----|

Caller will assume data points were not written and could start a retry operation which amplifies the load on KairosDB.