Allow a PeerDist hosted cache server to be specified via the
${peerhost} setting, e.g.:

  # Use 192.168.0.1 as hosted cache server
  set peerhost 192.168.0.1

Note that this simply treats the hosted cache server as a permanently
discovered peer for all segments.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

Record and report the number of peers (calculated as the maximum
number of peers discovered for a block's segment at the time that the
block download is complete), and the percentage of blocks retrieved
from peers rather than from the origin server.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

Signed-off-by: Michael Brown <mcb30@ipxe.org>

Signed-off-by: Michael Brown <mcb30@ipxe.org>