qemurunner: add boot logs to do_testimage task logs in real time

Complex boot sequences take a lot of time to reach serial console login.
In our case boot involves multiple bootloaders like u-boot and grub,
then hypervisors like xen, then initramfs images which do things like
validating secure boot and encrypting the main rootfs. All these happen
before main rootfs serial console login prompt is reached and thus many
things can go wrong, including race conditions, hangs and deadlocks, and
thus logging the details is important for development.

This change adds the qemu serial console logs to do_testimage task logs while
they are being read out. The logs are not added to bitbake output. This
enables debugging and tracing the do_testimage via task log file while the boot
and tests are running.

(From OE-Core rev: cb62fae6ea3e411643395b12e56c363ce4d73e5d)

Signed-off-by: Mikko Rapeli <mikko.rapeli@linaro.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/utils/qemurunner.py

@@ -480,6 +480,7 @@ class QemuRunner:
                         self.logger.error('Invalid file type: %s\n%s' % (file))
                         read = b''
 
+                    self.logger.debug2('Partial boot log:\n%s' % (read.decode('utf-8', errors='ignore')))
                     data = data + read
                     if data:
                         bootlog += data