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 <rajpratik71@gmail.com>
