data4es: missed values (Stage 009: delay)

[mgolosova]

Motivation

Currently, data flow from Oracle to ES runs every hour, and some "empty" records appear in ES now and then.
I made sure that it runs in a proper environment and that the SQL query is fixed (see PR #110), yet they keep on appearing in the new data.
I suspect it can happen due to the fact that in the original database some data can appear with a delay, while the timestamp value for them is defined not by the database, but on previous steps.

Suggestion

When started with None "final timestamp" parameter, Connector tries to pull data "from X until Right Now".
I think what we need is to add new config parameter: timestamps.delay with default value, say, 1m (or better 5m), and teach Stage 009 to pull data "from X until Right Now minus delay".