Add statsite to basenode AMI.

This should setup and configure statsite in the basenode AMI if the `statsite` configuration is present in the userdata at instance boot time. I've largely copied this from the same changesets from the storm chef kitchen.

I unfortunately don't have anyway to test this at the moment since my AMI creation environment is out of date. @johnclaus and @librato-peter  -- can you spin this up in our new AMI environment and test it out?

The corresponding statsite configuration details have been added to the l2met data scripts: http://git.io/uOLvBQ. Once this AMI is popped, booting the new AMI with the new data files should configure and enable statsite.

/cc @collinvandyck