disable run_epoch_in_child_process in default (#901)

Author: fsx950223

efficientdet/main.py

@@ -111,7 +111,7 @@
 
 # for train_and_eval mode
 flags.DEFINE_bool(
-    'run_epoch_in_child_process', True,
+    'run_epoch_in_child_process', False,
     'This option helps to rectify CPU memory leak. If True, every epoch is '
     'run in a separate process for train and eval and memory will be cleared.'
     'Drawback: need to kill 2 processes if trainining needs to be interrupted.')