oeqa/qemurunner: Use oe._exit(), not sys.exit()

sys.exit will cause finally statements and other code to run at exit. Since
we're using os.fork() here, os._exit() is apprioriate in this codepath.

(From OE-Core rev: 2130363c7a8762866b523e596adf44ab63f40722)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit ec08498ff29de9ccd23be88b9d7af3dab6bbb81e)
Signed-off-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/utils/qemurunner.py

@@ -234,7 +234,7 @@ class QemuRunner:
             r = os.fdopen(r)
             x = r.read()
             os.killpg(os.getpgid(self.runqemu.pid), signal.SIGTERM)
-            sys.exit(0)
+            os._exit(0)
 
         self.logger.debug("runqemu started, pid is %s" % self.runqemu.pid)
         self.logger.debug("waiting at most %s seconds for qemu pid (%s)" %