oeqa qemurunner: read more data at a time from serial

Use a short sleep to bundle serial console reads so that
we are not reading one character at a time which reduces busy
looping.

(From OE-Core rev: cafe65d8cf7544edbd387f7f5f6d77c64c6b18fa)

Signed-off-by: Mikko Rapeli <mikko.rapeli@linaro.org>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/utils/qemurunner.py

@@ -468,6 +468,8 @@ class QemuRunner:
                     socklist.remove(self.server_socket)
                     self.logger.debug("Connection from %s:%s" % addr)
                 else:
+                    # try to avoid reading only a single character at a time
+                    time.sleep(0.1)
                     data = data + sock.recv(1024)
                     if data:
                         bootlog += data