Added NetAppCollector

Added NetAppCollector. This collects performance metrics from a NetApp using their Python API. These are a lot of metrics that are only available through the API, and not via eg. SNMP.
We've been running this collecting metrics from our NetApp boxes for a few months, and it appears to be working well.
I'm know there's much that can be improved in the code, but I wanted to get it out there for those that want to collect metrics from their NetApp storage systems. :-)