Before this change, index_html for Catalog Tool was None that means trying to
access view for CatalogTool from UI always make a function call to the
__call__ which function was overridden with searchResults, which
means everytime someone tried to access portal_catalog/, a useless query was
being made and an undesirable query result was displyed on the UI.
In this case, index_html is prefered whenever we try to access portal_catalog
from UI.
Also, add test for proper display of view when CatalogTool is accessed from XHTML UI