Making MemberEPR optional

["Vambenepe, William N" <vbp@hp.com>]

As requested on the conf last this week, here is an example of why one
might want to use a service group w/o providing an EPR for the members:

- A company does not want to expose direct access to its printers from
outside the firewall but it wants to externally expose a service group
listing them for their supplier (e.g. Staples).

Or

- There is a well-known way that service EPRs are retrieved (like a
directory) and the service group doesn't want to duplicate this
information.

Regards,

William