[RFE] Provide a mechanism to configure behavior of azure-init at runtime

[anhvoms]

Currently this is not a major issue as we don't have a lot of configurable options. However, as we start adding more features to make azure-init more useful and robust (such as logging, retries), we might need to provide a way for the users to configure azure-init behavior (such as where to put logging, the level of logging that should go to console, how many minutes to retry, etc...)

We can consider providing a config file in /etc/azure-init/azure-init.conf