[Libvir] [PATCH] check file format in virsh attach/detach-device

Hi virsh attach/detach-devich does not check file format now. This patch checks config file format is XML or not. (in virsh attach/detach-device) If file format is not XML, just return the error with message. Signed-off-by: Masayuki Sunou <fj1826dm@aa.jp.fujitsu.com> Atsushi SAKAI <sakaia@jp.fujitsu.com> Thanks, Masayuki Sunou.