selftest/runqemu: Handle SystemExit

The sigchld handler in runqemu can raise a SystemExit when qemu shuts down.
Rather than backtracing, accept this as a successful test result.

ERROR: runqemu.QemuTest.test_qemu_can_shutdown (subunit.RemotedTestCase)
testtools.testresult.real._StringException: Traceback (most recent call last):
  File "/home/pokybuild/yocto-worker/nightly-oe-selftest/build/meta/lib/oeqa/selftest/cases/runqemu.py", line 183, in test_qemu_can_shutdown
    qemu_shutdown_succeeded = self._start_qemu_shutdown_check_if_shutdown_succeeded(qemu, shutdown_timeout)
  File "/home/pokybuild/yocto-worker/nightly-oe-selftest/build/meta/lib/oeqa/selftest/cases/runqemu.py", line 175, in _start_qemu_shutdown_check_if_shutdown_succeeded
    time.sleep(1)
  File "/home/pokybuild/yocto-worker/nightly-oe-selftest/build/meta/lib/oeqa/utils/qemurunner.py", line 100, in handleSIGCHLD
    raise SystemExit
SystemExit

(From OE-Core rev: 417245923c1c2c35a60d6db29cbe5a78548860d2)

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

meta/lib/oeqa/selftest/cases/runqemu.py

@@ -166,14 +166,17 @@ class QemuTest(OESelftestTestCase):
         # when qemu was shutdown by the above shutdown command
         qemu.runner.stop_thread()
         time_track = 0
-        while True:
-            is_alive = qemu.check()
-            if not is_alive:
-                return True
-            if time_track > timeout:
-                return False
-            time.sleep(1)
-            time_track += 1
+        try:
+            while True:
+                is_alive = qemu.check()
+                if not is_alive:
+                    return True
+                if time_track > timeout:
+                    return False
+                time.sleep(1)
+                time_track += 1
+        except SystemExit:
+            return True
 
     def test_qemu_can_shutdown(self):
         self.assertExists(self.qemuboot_conf)