traffic: generate more statistics in replay

traffic: generate more statistics in replay

Add more "header" values indicating the progress of the run as a
whole.

The new fields are:

Max sleep miss            - the longest sleep() oversleep. Indicates client load.
Maximum lag               - the longest gap between a planned packet
                            time and its actual time.
Start lag                 - the longest gap between intended and actual
                            conversation start.
Planned conversations     - how many conversations we meant to have.
Planned packets           - how many "packets" we thought we were making. Not
                            all "packets" result in actual operations or packets.
Unfinished conversations  - how many conversations had not finished
                            when they were killed.

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>