This commit swaps the partition field to the local partition for
discovery chains targeting peers. Prior to this change, peer upstreams
would always use a value of default regardless of which partition they
exist in. This caused several issues in xds / proxycfg because of id
mismatches.
Some prior fixes were made to deal with one-off id mismatches that this
PR also cleans up, since they are no longer needed.
Derek Menteer