Update verify_agent_os.py
Update verify_agent_os.py

* Allow to pass the VMImageName and keep the mapping logic between image names and friendly names in this script
* Set the OSName variable based on the result of this script running

tg-msft/azure-sdk-tools,tg-msft/azure-sdk-tools,tg-msft/azure-sdk-tools,tg-msft/azure-sdk-tools,tg-msft/azure-sdk-tools,tg-msft/azure-sdk-tools,tg-msft/azure-sdk-tools,tg-msft/azure-sdk-tools