Add an epoch limit for training.
Add an epoch limit for training.

coded5282/youtube-8m,slai11/youtube-8m,hxkk/u8m_test,slai11/youtube-8m,forwchen/yt8m,google/youtube-8m,lidalei/youtube-8m,KangHsi/youtube-8m,slai11/youtube-8m,mwoodson1/youtube-8m-competition,KangHsi/youtube-8m,slai11/youtube-8m,forwchen/yt8m