refactor: use shlex to quote QEMU boot args

Signed-off-by: Felix Zwettler <Felix.Zwettler@duagon.com>

Author: flxzt

labgrid/driver/qemudriver.py

@@ -225,7 +225,7 @@ def get_qemu_base_args(self):
             boot_args.append(self.boot_args)
         if self.kernel is not None and boot_args:
             cmd.append("-append")
-            cmd.append("\'" + " ".join(boot_args) + "\'")
+            cmd.append(shlex.quote(" ".join(boot_args)))
 
         return cmd