Add mpi4py to pip installs (aws#185)

Author: laurenyu

.gitignore

@@ -6,9 +6,5 @@ dist
 *.iml
 **/.ipynb_checkpoints
 **/.python-version
-<<<<<<< HEAD
 .tox
 *~
-=======
-.tox
->>>>>>> Add Horovod benchmark (#157)

docker/1.12.0/Dockerfile.gpu

@@ -112,10 +112,7 @@ COPY $framework_support_installable .
 
 RUN pip install --no-cache-dir -U \
     keras==2.2.4 \
-<<<<<<< HEAD
     mpi4py==3.0.1 \
-=======
->>>>>>> Add SageMaker integ test for hyperparameter tuning model_dir logic (#183)
     $framework_support_installable \
     "sagemaker-tensorflow>=1.12,<1.13" \
     # Let's install TensorFlow separately in the end to avoid