message: change import-mode for release.test
diff: @@ -39,7 +39,7 @@ else
  python3 -m pip install wheelhouse/*-cp${CPYTHON_VERSION}-*.whl
  fi
  python3 -m pip install -q pytest boto3 pyarrow==0.11.1 pandas==0.19.2
  -(cd tests && python3 -m pytest .)
  +(cd tests && python3 -m pytest --import-mode=append .)
  CPYTHON_VERSION=$(python -c 'import sys; print(str(sys.version_info[0])+str(sys.version_info[1]))')
  if [[ ! -z ${TENSORFLOW_INSTALL} ]]; then
  @@ -49,6 +49,6 @@ else
  python -m pip install wheelhouse/*-cp${CPYTHON_VERSION}-*.whl
  fi
  python -m pip install -q pytest boto3 pyarrow==0.11.1 pandas==0.19.2
  -(cd tests && python -m pytest .)
  +(cd tests && python -m pytest --import-mode=append .)
  (cd R-package && R -e 'stopifnot(all(data.frame(devtools::test())$failed == 0L))')
  