optimize size and time using "--no-cache-dir"

optimize size and time using "--no-cache-dir"

Using "--no-cache-dir" flag in pip install ,make sure dowloaded packages
by pip don't cached on system . This is a best practise which make sure
to fetch ftom repo instead of using local cached one . Further , in case
of Docker Containers , by restricing 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: INT-1616

Signed-off-by: Pratik Raj <rajpratik71@gmail.com>
Change-Id: Id3e28faf35f36258362323b4a96bcf0f3f95726b
Signed-off-by: mrichomme <morgan.richomme@orange.com>