Fix setting of PARLAI_DATAPATH and PARLAI_DOWNPATH env variables (#1668)
Fix setting of PARLAI_DATAPATH and PARLAI_DOWNPATH env variables (#1668)

* fix params for download path and data path

* merge master

* merge2

* comment for behavior

facebookresearch/ParlAI,facebookresearch/ParlAI,facebookresearch/ParlAI,facebookresearch/ParlAI,facebookresearch/ParlAI