use --no-cache-dir flag to pip in dockerfiles to save space

using "--no-cache-dir" flag in pip install ,make sure downloaded packages
by pip don't cached on system . This is a best practice which make sure
to fetch from repo instead of using local cached one . Further , in case
of Docker Containers , by restricting caching , we can reduce image size.
In term of stats , it depends upon the number of python packages
multiplied by their respective size . e.g for heavy packages with a lot
of dependencies it reduce a lot by don't caching pip packages.

Further , more detail information can be found at

https://medium.com/sciforce/strategies-of-docker-images-optimization-2ca9cc5719b6

Signed-off-by: Pratik raj <[email protected]>

applications/openvino/benchmark/Dockerfile

@@ -51,7 +51,7 @@ RUN wget $OPENVINO_LINK && \
         rm -rf /tmp/l_openvino_toolkit* && \
         ln --symbolic /opt/intel/openvino_"$YEAR"/ /opt/intel/openvino
 
-RUN pip3 install networkx==2.3
+RUN pip3 install --no-cache-dir networkx==2.3
 WORKDIR /opt/intel/openvino_$YEAR/deployment_tools/demo
 RUN /bin/bash -c "source $INSTALL_DIR/bin/setupvars.sh && ./demo_squeezenet_download_convert_run.sh"
 WORKDIR /root/inference_engine_samples_build
@@ -70,7 +70,7 @@ USER openvino
 #Download OpenVINO pre-trained models
 
 WORKDIR /opt/intel/openvino_$YEAR/deployment_tools/open_model_zoo/tools/downloader
-RUN pip3 install pyyaml requests
+RUN pip3 install --no-cache-dir pyyaml requests
 RUN ./downloader.py  --name face-detection-retail-0004
 RUN ./downloader.py  --name squeezenet1.1
 RUN ./downloader.py  --name semantic-segmentation-adas-0001

iot-gateway/baidu-openedge/scripts/ansible/examples/setup_baidu_openedge/composefile/Dockerfile

@@ -31,7 +31,7 @@ RUN python3.6 get-pip.py
 
 # needed by openedge when build
 RUN apk add --no-cache zip unzip tcpdump 
-RUN pip3 install protobuf 
+RUN pip3 install --no-cache-dir protobuf 
 
 RUN ln -sf /usr/share/zoneinfo/Asia/Shanghai /etc/localtime
 RUN echo 'Asia/Shanghai' >/etc/timezone
@@ -45,7 +45,7 @@ RUN apk add --no-cache musl-dev
 #WORKDIR /root/
 
 # install python pip and grpcio
-#RUN pip install protobuf grpcio
+#RUN pip install --no-cache-dir protobuf grpcio
 
 # install golang 
 RUN apk add --no-cache go bash