autotest/autotest — pull request #487 by ypu (2012-08-01 09:14:08+00:00)
Title: virt: Add option log_func to QemuIO

Add option log_func to QemuIO to help user to record the
informations in different levels.
Also fix the problem caused by the scripts will try to call
output_func when it is None.

Signed-off-by: Yiqiao Pu