script: Add 'random-seed' option to traffic_replay

script: Add 'random-seed' option to traffic_replay

When using a traffic-model file to generate traffic, there is some
randomness in the actual packets that get generated. This means it's
hard to use the tool to detect an increase/decrease in Samba
performance - we don't know whether a decrease in packets sent is due
to a regression in the Samba codebase, or just due to the tool sending
different types of packets (i.e. ones that take longer to process).

This patch adds an option to seed the python random number generator.
This means that exactly the same traffic can be generated across
multiple test runs.

(Previously we were using the '--traffic-summary' option to avoid this
problem - we can generate a summary-file based on the model, and then
use the same summary file across multiple runs. However, this proved
impractical when you want to run multiple combinations of scale/rate
parameters, e.g. 21 x 8 different permutations just fills up disk space
with summary-files.)

Signed-off-by: Tim Beale <timbeale@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Alexander Bokovoy <ab@samba.org>
Reviewed-by: William Brown <william@blackhats.net.au>
Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Wed May 16 13:53:26 CEST 2018 on sn-devel-144