Frisbee master server compatibility mode fix for vnodes.
The mserver wants to validate nodes by looking up their IP address in the interfaces table, and vnodes have no interfaces table entries. So when we invoke the frisbeehelper in compat mode, do so with the pnode identity instead. For validation purposes, this is identical. Is this an issue for non-compat mode? Not right now since all our vnode implementations that load images make their loadinfo request from the physical host. If vnodes start to call the master server on boss directly, we will have an issue.