Add an mnist example for estimator scripts. Fixed some bugs

6 jobs for monitored_training in 10 minutes and 1 second (queued for 13 seconds)
Status Job ID Name Coverage
  Build
passed #96468
conda-linux
build_linux_27

00:02:33

passed #96469
conda-linux
build_linux_35

00:02:35

passed #96470
conda-linux
build_linux_36

00:02:14

 
  Test
passed #96471
conda-linux
test_linux_27

00:06:27

66.0%
passed #96472
conda-linux
test_linux_35

00:07:24

66.0%
passed #96473
conda-linux
test_linux_36

00:07:05

66.0%