Non-glance images with same href are considered to be the same

[Vladyslav Drok]

Currently, if a non-glance image is used, its contents may be updated, but Ironic won't notice it and won't redownload the image.

This problem can be solved by checking modification date for file:// images, and for http(s):// images, last-modified header could be used to determine whether image inside cache is outdated or not.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/195017
Committed: https://git.openstack.org/cgit/openstack/ironic/commit/?id=19165ceba62c2f443385a2f92321b4ddf482cfa6
Submitter: Jenkins
Branch: master

commit 19165ceba62c2f443385a2f92321b4ddf482cfa6
Author: Vladyslav Drok <email address hidden>
Date: Mon Jun 22 11:56:14 2015 -0400

    Update cached images based on update time

    Currently, if non-glance image is used in ironic, and contents of this
    image are updated on HTTP(S) server or on file system available
    locally (except for the case when it is the file system where image
    cache is located), ironic won't be able to determine that the image
    was updated and will not update the cache.

    In this change it is proposed to use last modification date to
    determine if an image is up to date. For file system it can be
    accomplished with standard operating system means, and for HTTP(S)
    images 'Last-Modified' HTTP header can be used.

    Closes-bug: #1459328
    Change-Id: Ia3e6b6072fdf7a4bfffdc3fbaf31103605c7ff5b