Add horovod estimator save/load/get_models/shutdown (intel-analytics#…

…2702)

* add get_model/save/load/shutdown for pytorch horovod estimator

* change args

* remove condition

* change name

* remove get multiple models

* add pytorch estimator ut and disable for now

* meet comments

python/orca/test/dev/run-pytests-ray

@@ -34,7 +34,8 @@ then
 fi
 
 echo "Running orca learn ray tests"
-python -m pytest -v ../test/zoo/orca/learn/ray
+python -m pytest -v ../test/zoo/orca/learn/ray \
+       --ignore=../test/zoo/orca/learn/ray/pytorch/test_pytorch_estimator.py
 exit_status_2=$?
 if [ $exit_status_2 -ne 0 ];
 then