LU-16502 python: improve support for virtual environments

Python virutal environments make it easy to install the
correct Python packages isolated from the rest of the
system.

 https://docs.python.org/3/library/venv.html



.venv is added to .gitignore and a simple virtual environment
example has been added to the README.

This patch collects all of the requirements for various
scripts in the Lustre tree and consolidates them in a
top level requirements.txt. lu_object.py spacing was
fixed due to parsing errors.

Test-Parameters: trivial
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: I69d074e9ba50022817bd243fb82d004366ab6adf
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/53209


Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>