Fix orca ray pytorch example (#3007)
Fix orca ray pytorch example (#3007)

* fix horovod pytorch exampe

* fix bug

* fix process group

* fix style

* fix tests

* fix test

* fix tests

* revert ray context change
yangw1234/BigDL,intel-analytics/BigDL,intel-analytics/BigDL,intel-analytics/BigDL,yangw1234/BigDL,yangw1234/BigDL,intel-analytics/BigDL,yangw1234/BigDL