Add Horovod tests (#2761)
Add Horovod tests (#2761)

* add pytorch horovod tests

* add horovod tf tests

* fix

* fix style

* fix tests

* fix tests

* fix tests

* fix tests

* fix tests

* fix tests
intel-analytics/BigDL,yangw1234/BigDL,yangw1234/BigDL,yangw1234/BigDL,intel-analytics/BigDL,yangw1234/BigDL,intel-analytics/BigDL,intel-analytics/BigDL