swift-recon: Added oldest and most recent repl

I've been doing this with cluster-wide log searches for far too long.
This adds support for reporting the oldest replication pass
completion as well as the most recent. This is quite useful for
finding those odd replicators that have hung up for some reason and
need intervention.

Change-Id: I7fd7260eca162d6b085f3e82aaa3cf90670f2d53
Merge "swift-recon: Added oldest and most recent repl"