allow the user to manage "snappi_ixnetwork" logger

[mtache]

Is your feature request related to a use case? Please describe.
Currently, the snappi_ixnetwork.logger.setup_ixnet_logger function configure the snappi_ixnetwork with a StreamHandler and optional FileHandler.
This prevent from using snappi_ixnetwork as a library in a Python application where we want to have control over the logging handlers.

Describe the solution you'd like
Do not modify the snappi_ixnetwork logger if it already has handlers configured. Like this is being done here: https://github.com/OpenIxia/ixnetwork_restpy/blob/master/ixnetwork_restpy/connection.py#L96

Describe alternatives you've considered
For now, I am using a forked snappi_ixnetwork library to build my application.