Increase default page_size value

This is a temporary solution. Increasing the default page size (which is being
used everytime, since the client is ignoring nova's --limit param). This should
decrease the number of queries that glance does when nova requests an image
detail list.

Bug 1200257

Change-Id: I7ed4521698570cbae9c20e69ddca8b11b57c65ad
Merge "Increase default page_size value"