bootdevice: bug fixes

# gpg: Signature made Tue Mar  3 05:18:39 2015 GMT using RSA key ID DDE30FBB
# gpg: Good signature from "Gonglei <arei.gonglei@huawei.com>"
# gpg: WARNING: This key is not certified with a trusted signature!
# gpg:          There is no indication that the signature belongs to the owner.
# Primary key fingerprint: 5178 9C82 617F 2F58 8693  63B1 BA7A 65B0 DDE3 0FBB

* remotes/gonglei/tags/bootdevice-next-20150303:
  bootdevice: add check in restore_boot_order()
  bootdevice: check boot order argument validation before vm running
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>