MINOR: cfgparse/peers: provide more info when ignoring invalid "peer" or "server...

MINOR: cfgparse/peers: provide more info when ignoring invalid "peer" or "server" lines

Invalid (incomplete) "server" or "peer" lines under peers section are now
properly ignored. For completeness, in this patch we add some reports so
that the user knows that incomplete lines were ignored.

For an incomplete server line, since it is tolerated (see GH #565), we
only emit a diag warning.

For an incomplete peer line, we report a real warning, as it is not
expected to have a peer line without an address:port specified.

Also, 'newpeer == curpeers->local' check could be simplified since
we already have the 'local_peer' variable which tells us that the
parsed line refers to a local peer.