MNIST tutorial: fix so it can run internally + cleanup
MNIST tutorial: fix so it can run internally + cleanup

Summary: I made it use ~/caffe2_notebooks instead of polluting the repo dirrectly. Symlinking stuff into the repo makes buck crazy and so does having any level db files in there. So I would really preffer keeping working dirrectory for ipython outside of it.

Reviewed By: Yangqing

Differential Revision: D4945235

fbshipit-source-id: b8d1212dd82dcaa2c531e8c64900cc352ccfb3d7

bwasti/caffe2,sf-wind/caffe2,Yangqing/caffe2,bwasti/caffe2,sf-wind/caffe2,sf-wind/caffe2,pietern/caffe2,pietern/caffe2,xzturn/caffe2,pietern/caffe2,sf-wind/caffe2,Yangqing/caffe2,xzturn/caffe2,davinwang/caffe2,Yangqing/caffe2,davinwang/caffe2,bwasti/caffe2,xzturn/caffe2,pietern/caffe2,Yangqing/caffe2,sf-wind/caffe2,davinwang/caffe2,xzturn/caffe2,pietern/caffe2,davinwang/caffe2,Yangqing/caffe2,caffe2/caffe2,xzturn/caffe2,bwasti/caffe2,davinwang/caffe2,bwasti/caffe2