Touch in use image files when they're checked.

It was intended that FLAGS.remove_unused_resized_minimum_age_seconds
would indicate the number of seconds a base file was unused before it
was removed. This however isn't true at the moment. Because instances
are COW mostly, this will be the time since the resize occurred,
which is normally instantly true once the image isn't being used any
more. This small patch corrects that by touching the base image during
check cycles which find it in use. Resolves bug 967845.

Change-Id: I75bf06cf758c9a2d7a8bde5ce67c789d7e299174

nova/tests/test_imagecache.py

@@ -562,6 +562,10 @@ class ImageCacheManagerTestCase(test.TestCase):
 
         self.stubs.Set(os.path, 'exists', lambda x: exists(x))
 
+        # We need to stub utime as well
+        orig_utime = os.utime
+        self.stubs.Set(os, 'utime', lambda x, y: None)
+
         # Fake up some instances in the instances directory
         orig_listdir = os.listdir