This is the OSS portion of enterprise PR 2352.
It adds a server-local implementation of the proxycfg.PeeredUpstreams interface
based on a blocking query against the server's state store.
It also fixes an omission in the Virtual IP freeing logic where we were never
updating the max index (and therefore blocking queries against
VirtualIPsForAllImportedServices would not return on service deletion).
Daniel Upton