tests: Work audit_log CLIENT_IP out from config instead of env var

tests: Work audit_log CLIENT_IP out from config instead of env var

Instead of passing the CLIENT_IP to the audit_log tests, we can just
work out the source-IP that the client will use from its smb.conf file.
Because the audit_log tests are all run on the non-local testenv,
they'll already use the client.conf and the 127.0.0.11 address.

The main advantage of this change is it avoids having hardcoded IP
addresses in the selftest framework.

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