Move IP to attributes to allow override elsewhere

This allows the agent's own IP Address to be configurable in a wrapper cookbook or elsewhere.  For example, a user may want to configure zabbix to communicate on a separate network and thus the node's IP would be different.  Much of this configuration could also be done in Ohai with a plugin, however I think this also adds some easily configurable value, especially in use cases such as test kitchen overrides. If this was left out intentionally, I'm all ears for other suggestions!