message: Install tf-nightly before trying to install Horovod.
diff: # ==============================================================================
  set -e
  +# TODO(pkanwar): upgrade to 3.7.
  +PIP_CMD="pip3.5"
  +
  # Source the external common scripts.
  source tensorflow/tools/ci_build/release/common.sh
  -
  # Install latest bazel
  install_bazelisk
  which bazel
  +# Install pip3.5
  +curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py
  +sudo python3.5 get-pip.py
  +
  # Install realpath
  sudo apt-get install realpath
  -# Update the version string to nightly
  -if [ -n "${IS_NIGHTLY_BUILD}" ]; then
  - ./tensorflow/tools/ci_build/update_version.py --nightly
  -fi
  +# Install tf-nightly and verify version.
  +"${PIP_CMD}" install --user tf-nightly
  +
  +python3.5 -c "import tensorflow as tf; print(tf.__version__)"
  # Download and install open-mpi.
  wget https://download.open-mpi.org/release/open-mpi/v4.0/openmpi-4.0.4.tar.gz
  @@ -50,17 +56,17 @@ sudo ldconfig
  # Install Horovod.
  cd ..
  -pip3 install horovod tensorflow
  +"${PIP_CMD}" install horovod tensorflow
  # Install tests.
  git clone https://github.com/DEKHTIARJonathan/TF_HVD_Stability_Test.git
  # Install pytest.
  -pip3 install -U pytest
  +"${PIP_CMD}" install -U pytest
  # Install requirements.
  cd TF_HVD_Stability_Test
  -pip3 install -r requirements.txt
  +"${PIP_CMD}" install -r requirements.txt
  # Run the tests.
  -python3 -m pytest
  +python3.5 -m pytest
  