qemurunner: Clean up serial_lock handling

Avoid "RuntimeError: release unlocked lock" since the lock shouldn't
be locked even in the error path. Add a try/finally path to ensure
this.

(From OE-Core rev: b0732ee009ca47580d1d2ad75334f4aa50e6efd5)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/utils/qemurunner.py

@@ -521,7 +521,6 @@ class QemuRunner:
                 except Exception as e:
                     self.logger.warning('Extra log data exception %s' % repr(e))
                     data = None
-            self.thread.serial_lock.release()
             return False
 
         with self.thread.serial_lock:
@@ -824,10 +823,12 @@ class LoggingThread(threading.Thread):
                     self.logfunc(data, ".stdout")
                 elif self.serialsock and self.serialsock.fileno() == fd:
                     if self.serial_lock.acquire(blocking=False):
-                        data = self.recv(1024, self.serialsock)
-                        self.logger.debug("Data received serial thread %s" % data.decode('utf-8', 'replace'))
-                        self.logfunc(data, ".2")
-                        self.serial_lock.release()
+                        try:
+                            data = self.recv(1024, self.serialsock)
+                            self.logger.debug("Data received serial thread %s" % data.decode('utf-8', 'replace'))
+                            self.logfunc(data, ".2")
+                        finally:
+                            self.serial_lock.release()
                     else:
                         serial_registered = False
                         poll.unregister(self.serialsock.fileno())