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

@@ -40,14 +40,14 @@ RUN $INSTALL_DIR/install_dependencies/install_openvino_dependencies.sh
 RUN mkdir $INSTALL_DIR/deployment_tools/inference_engine/samples/cpp/build 
 WORKDIR $INSTALL_DIR/deployment_tools/inference_engine/samples/cpp/build
 RUN /bin/bash -c "source $INSTALL_DIR/bin/setupvars.sh && cmake .. && make -j1"
-RUN pip3 install networkx==2.3
+RUN pip3 install --no-cache-dir networkx==2.3
 
 WORKDIR /opt/intel/openvino/deployment_tools/demo
 RUN /bin/bash -c "source $INSTALL_DIR/bin/setupvars.sh && ./demo_squeezenet_download_convert_run.sh"
 
 #Download OpenVINO pre-trained models
 
-RUN pip3 install pyyaml requests
+RUN pip3 install --no-cache-dir pyyaml requests
 WORKDIR /opt/intel/openvino/deployment_tools/open_model_zoo/tools/downloader
 RUN ./downloader.py  --name face-detection-retail-0004
 RUN ./downloader.py  --name squeezenet1.1

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

@@ -11,7 +11,7 @@ RUN yum install -y python36-pip
 
 # needed by openedge when build
 RUN yum install -y zip unzip tcpdump 
-RUN pip3 install grpcio protobuf pyyaml
+RUN pip3 install --no-cache-dir grpcio protobuf pyyaml
 
 
 #RUN yum install -y wget python iputils-ping python-pip openssh-server expect iperf3 net-tools openssh-clients psmisc
@@ -21,7 +21,7 @@ RUN yum install -y make git
 WORKDIR /root/
 
 # install python pip and grpcio
-#RUN pip install protobuf grpcio
+#RUN pip install --no-cache-dir protobuf grpcio
 
 # install golang 
 RUN wget https://dl.google.com/go/go1.11.4.linux-amd64.tar.gz