[CAY-1257] Fix to do checkpoint the model at last epoch

[wynot12]

Resolves #1257

This PR resolves the problem in #1257.

[yunseong]

Below is an example:

• (before)

  200 2017-11-14 21:05:35,230 INFO cay.dolphin.async.BatchProgressTracker.onProgressMsg pool-9-thread-8 | Checkpoint model table. EpochIdx: 0
  ...
  204 2017-11-14 21:05:35,274 INFO cay.dolphin.async.BatchProgressTracker.onProgressMsg pool-9-thread-8 | Batch progress: 24 / 75.

• (after)

  189 2017-11-14 21:22:35,086 INFO cay.dolphin.async.BatchProgressTracker.onProgressMsg pool-9-thread-7 | Batch progress: 25 / 75.
  190 2017-11-14 21:22:35,086 INFO cay.dolphin.async.BatchProgressTracker.onProgressMsg pool-9-thread-7 | Checkpoint model table. EpochIdx: 1

[wynot12]

Great! Thanks for refinement :)