tests: Make IPv4 assumption explicit

tests: Make IPv4 assumption explicit

This test is asserting the expected number of *IPv4* addresses, not any
interface address (including IPv6). It works currently because the
selftest client doesn't have an IPv6 address in its smb.conf.

This patch makes the IPv4 assumption explicit by importing
interface_ips_v4() from the provision code. We need to tweak this to
pass through an 'all_interfaces' flag, otherwise it filters out the
loopback IP addresses that the testenv is using.

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