support/testing: use qemu stdio in emulator

support/testing: use qemu stdio in emulator

Instead of redirecting qemu serial to telnet, redirect it to stdio.

It allows to run testcases in parallel without random failing caused by
two emulators trying to use the same telnet port (1234).

'qemu -serial stdio' returns some extra <CR> characters, so remove them
from the log.

Signed-off-by: Ricardo Martincoski <ricardo.martincoski@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>