tests: use g_test_rand_int

tests: use g_test_rand_int

g_test_rand_int provides a reproducible random integer number, using a
different number seed every time but allowing reproduction using the
--seed command line option.  It is thus better suited to tests than
g_random_int or random.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <1576113478-42926-1-git-send-email-pbonzini@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>