[API] Training API with generator

[API] Training API with generator

There is no API to get training, validation, test data from generator
function.

In this PR, introduces new training API with generator function.
. New Tizen API.
. Add Unit Test API with generator function.
. Add Test generator for future test.

**Self evaluation:**
1. Build test:	 [X]Passed [ ]Failed [ ]Skipped
2. Run test:	 [X]Passed [ ]Failed [ ]Skipped

Signed-off-by: jijoong.moon <jijoong.moon@samsung.com>