Added 'page_size' param to image list

Added a new query param called 'page_size' to
accepted_query_params list in image list call.
This param is passed on to glance-client which will
be used to paginate the result set.

Fixes bug 1200233

Change-Id: I1c804c74c153e80bb572ec45283ebd9b6b7b41c5
Merge "Added 'page_size' param to image list"