Comment 2 for bug 1700926

Reviewed: https://review.openstack.org/478429
Committed: https://git.openstack.org/cgit/openstack/os-xenapi/commit/?id=7ac84ec31dd1df6af90b2bf333253848cb4de2c3
Submitter: Jenkins
Branch: master

commit 7ac84ec31dd1df6af90b2bf333253848cb4de2c3
Author: naichuans <email address hidden>
Date: Wed Jun 28 08:19:03 2017 +0000

    os-xenapi: Exception Error logs shown in Citrix XenServer CI

    There are many errors in the patchs which passed our XenServer CI,
    it is because when run tempest, test case will ask nova sevice to
    do snapshotting, then delete image before snapshotting done. Then
    nova compute service couldn't find the image when do image upload
    and raise an exception.
    Normally the exception can be consumed by nova service. But the
    exception generated by os-xenapi can't be recognized by nova, so
    the error logs come out.

    Throw an exception XenAPI.Failure which computer service can process
    Add unit test to check XenAPI.Failure exception

    Change-Id: Ibe30a76f278264e0ddd1fc29d533fdeaab0a13a5
    Closes-Bug: 1700926