Split interface-rps script File resources to class

The interface-rps script file resource would cause duplicate definition
if more than one interface::rps resource was defined for a host. Fix
this by moving the File resource into its own class and require that
class in the definition. Add a comment about the above in order to avoid
future melding on the class into the define. This fixes a duplicate
definition issue introduced in ab47728

Change-Id: If76dbb328efe45de1ca803f36433b960aa6530aa