[SPARK-18620][STREAMING][KINESIS] Flatten input rates in timeline for streaming + kinesis

## What changes were proposed in this pull request?
This pr is to make input rates in timeline more flat for spark streaming + kinesis.
Since kinesis workers fetch records and push them into block generators in bulk, timeline in web UI has many spikes when `maxRates` applied (See a Figure.1 below). This fix splits fetched input records into multiple `adRecords` calls.

Figure.1 Apply `maxRates=500` in vanilla Spark
<img width="1084" alt="apply_limit in_vanilla_spark" src="https://cloud.githubusercontent.com/assets/692303/20823861/4602f300-b89b-11e6-95f3-164a37061305.png">

Figure.2 Apply `maxRates=500` in Spark with my patch
<img width="1056" alt="apply_limit in_spark_with_my_patch" src="https://cloud.githubusercontent.com/assets/692303/20823882/6c46352c-b89b-11e6-81ab-afd8abfe0cfe.png">

## How was this patch tested?
Add tests to check to split input records into multiple `addRecords` calls.

Author: Takeshi YAMAMURO <linguin.m.s@gmail.com>

Closes #16114 from maropu/SPARK-18620.