[Reviewer: Felix] Plivo

Felix, please can you review my chef script to create a Plivo node?  I'm not expecting you to review the config files (at least not in detail) - just the recipe, and associated knife tweaks.  Note that as part of this, I've introduced an internal-sip security group, of which bono, sprout and Perimeta are members.  This should remove the need for all the cross-references we have between their security groups but unfortunately I have to leave those in (at least for now) because you can't change the security groups applied to running instances.  I've tested this live.