Remove "image_cache_invalid_entry_grace_period "option

[Noboru Arai]

"image_cache_invalid_entry_grace_period " option is used glance-cache.conf, but the option is unused in *.py.

  <Result of "grep" command>
     vagrant@precise64:/opt/stack/glance$ grep -r image_cache_invalid_entry_grace_period ./
     ./etc/glance-cache.conf:# image_cache_invalid_entry_grace_period - seconds
     ./etc/glance-cache.conf:image_cache_invalid_entry_grace_period = 3600

because of https://review.openstack.org/#/c/1064/3/glance/image_cache/cleaner.py, I think the option is unused.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/55789

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/55789
Committed: http://github.com/openstack/glance/commit/3db3edabe6771f9d24e995720b82b600f3031386
Submitter: Jenkins
Branch: master

commit 3db3edabe6771f9d24e995720b82b600f3031386
Author: Noboru Arai <email address hidden>
Date: Mon Nov 11 15:03:56 2013 +0900

    Remove "image_cache_invalid_entry_grace_period" option

     "image_cache_invalid_entry_grace_period" option is unused
    in *.py, but the option is used in glance-cache.conf.

     I removed "image_cache_invalid_entry_grace_period" option
    from glance-cache.conf.

    Change-Id: Id235945f9cc89219118e4a3ec077f0e887a3b3ef
    Closes-Bug: #1249949