tester: another fix for log truncation
tester: another fix for log truncation

max_size / 10 returns a float.  Use // to return an integer, because
floats cannot be used as slice indices.

Signed-off-by: Paolo Bonzini <69d3ebcf5ee4e7f05a50dc23cd96655b730804b4@redhat.com>

pvital/patchew,pvital/patchew,pvital/patchew,pvital/patchew