add a new qevent: QEVENT_GUEST_PANICKED

This event will be emited when qemu detects guest panic.

Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-id: cf0bc45ecf9ecd3699bc72dc39f8cbab8ed79d8c.1366945969.git.hutao@cn.fujitsu.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
