deploy scalyr-agent as an optional role (#1987)

Initial chef recipe to deploy the scalyr agent.  Tested by repeated installs to app1.stage and util1.stage, and rebooting those machines.

Given that their operational stuff isn't completely solid just yet, instead of adding this to our mainline roles, I've created a new role.  We can then just put this on one prod machine to see if this has any impact on that machines performance or resource utilization.