oeqa/utils/qemurunner: Print output when failed to login

This is useful for debugging.

(From OE-Core rev: da527d73f5eeae0f29b5f99aab757491d3f87ec7)

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/utils/qemurunner.py

@@ -354,6 +354,7 @@ class QemuRunner:
             else:
                 self.logger.debug("Couldn't login into serial console"
                             " as root using blank password")
+                self.logger.debug("The output:\n%s" % output)
         except:
             self.logger.debug("Serial console failed while trying to login")
         return True