qemu.py: Add QEMUMachine.exitcode() method

Allow the exit code of QEMU to be queried by scripts.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20170526181200.17227-3-ehabkost@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

scripts/qemu.py

@@ -88,6 +88,11 @@ class QEMUMachine(object):
     def is_running(self):
         return self._popen and (self._popen.returncode is None)
 
+    def exitcode(self):
+        if self._popen is None:
+            return None
+        return self._popen.returncode
+
     def get_pid(self):
         if not self.is_running():
             return None