Clear the operator default engines before running operator tests
Clear the operator default engines before running operator tests

Reviewed By: akyrola

Differential Revision: D5729024

fbshipit-source-id: f2850d5cf53537b22298b39a07f64dfcc2753c75

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