fix timeouts in CloneOrCreateCommonWorld
fix timeouts in CloneOrCreateCommonWorld

Summary: Default value for timeout in CreateOrCloneCommonWorld does not work properly: if the value of dpm._DEFAULT_TIMEOUT is changed, the default still stays as old 30s. Changed to use None instead as default.

Reviewed By: pietern

Differential Revision: D5813228

fbshipit-source-id: f617ceec40a03893c27d3e13c426e1ca6b2114e2

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