io: bind to loopback IP addrs in test suite

The test suite currently binds to 0.0.0.0 or ::, which covers
all interfaces of the machine. It is bad practice for test
suite to open publically accessible ports on a machine, so
switch to use loopback addrs 127.0.0.1 or ::1.

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>