feat : use --no-cache-dir flag to pip in dockerfiles to save space (#792)

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

using the "--no-cache-dir" flag in pip install, make sure downloaded packages by pip don't cache on the system. This is a best practice that makes sure to fetch from a repo instead of using a local cached one. Further, in the case of Docker Containers, by restricting caching, we can reduce image size. In terms 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 reduces a lot by don't cache pip packages.

Further, more detailed information can be found at

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

Signed-off-by: Pratik Raj <rajpratik71@gmail.com>

* dont apply change to frozen images

Signed-off-by: Mikael Arguedas <mikael.arguedas@gmail.com>

---------

Signed-off-by: Pratik Raj <rajpratik71@gmail.com>
Signed-off-by: Mikael Arguedas <mikael.arguedas@gmail.com>
Co-authored-by: Mikael Arguedas <mikael.arguedas@gmail.com>

Author: Rajpratik71

docker/Dockerfile

@@ -3,7 +3,7 @@ FROM python:3
 WORKDIR /tmp/
 
 COPY requirements.txt .
-RUN pip install -r requirements.txt
+RUN pip install --no-cache-dir -r requirements.txt
 
 RUN git clone \
         -b master \