Fixing Dockerfile (#661)

Request pyarrow and opencv to be pip installed from binary.
(building pyarrow from source does not propeperly work in our container
and is not needed; opencv takes a long time to build, so binaries are ok)

docker/Dockerfile

@@ -42,15 +42,15 @@ RUN python3.6 -m pip install pip --upgrade
 RUN python3.6 -m pip install wheel
 RUN python3.6 -m venv /petastorm_venv3.6
 RUN /petastorm_venv3.6/bin/pip3.6 install --no-cache scikit-build
-RUN /petastorm_venv3.6/bin/pip3.6 install --no-cache -e /petastorm/[test,tf,torch,docs,opencv]
+RUN /petastorm_venv3.6/bin/pip3.6 install --no-cache -e /petastorm/[test,tf,torch,docs,opencv] --only-binary pyarrow --only-binary opencv-python
 RUN /petastorm_venv3.6/bin/pip3.6 uninstall -y petastorm
 
 # Set up Python3 environment
 RUN python3.7 -m pip install pip --upgrade
 RUN python3.7 -m pip install wheel
 RUN python3.7 -m venv /petastorm_venv3.7
 RUN /petastorm_venv3.7/bin/pip3.7 install --no-cache scikit-build
-RUN /petastorm_venv3.7/bin/pip3.7 install --no-cache -e /petastorm/[test,tf,torch,docs,opencv]
+RUN /petastorm_venv3.7/bin/pip3.7 install --no-cache -e /petastorm/[test,tf,torch,docs,opencv] --only-binary pyarrow --only-binary opencv-python
 RUN /petastorm_venv3.7/bin/pip3.7 uninstall -y petastorm
 
 # Clean up