[docker] use `--no-cache-dir` flag to `pip` in dockerfiles to save space

[docker] 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

Issue-ID: POLICY-2948
Signed-off-by: Pratik Raj <rajpratik71@gmail.com>
Change-Id: I0c4c6ba511bca93a1389c53a91bae9b2d4546ee6