traffic_replay: Make packet generation work on a pre-populated DB again

traffic_replay: Make packet generation work on a pre-populated DB again

Generate separate machine accounts for populating a large DB vs
replaying network traffic.

We want to use different userAccountControl flags in each of the above
cases (i.e. commit 3338a3e257fa9f28). However, this means that once you
use the --generate-users-only option, you can't replay network packets
against the machine accounts.

We can avoid this problem by creating separate machine accounts for each
of 2 different cases, e.g. STGM-0-x machines for traffic-replay, and
PC-0-x machines for padding out the database.

Signed-off-by: Tim Beale <timbeale@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>