Set page size when Glance API request is called

The glance related pollsters in central agent uses glanceclient to get
image-list from glance. Since glanceclient has pagination feature,
it calls glance API for every page sizes. When glanceclient is used by
Central Agent, default value of page size, that is 20, is used, since
Central Agent doesn't specify page size. However, default value of page
size is too small when there is a large number of images.

Therefore we need to specify page size from Central Agent.

Change-Id: I5f6457234a2963bbe567d078f2c8bb098c8a311c
Closes-bug: #1340577