glance: fix the ListImages method

Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>
examples: add the GlanceListImages example

This patch introduces a new example for the glance module. The example
authenticates to a known keystone instance to query the catalog and
retrieve the "image" (glance) services list.
Then it connects to the first glance instance and retrieves the list of
the available images.

Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>