InputScenarioUtils load images if glance available

The scenario_images utility of InputScenarioUtils shall
load the image list from glance only if glance is available.
Otherwise the test discovery process will fail if glance
is not available.

Closes bug 1277669

Change-Id: I4be7b9b88d9f8ff42059ece84a3c58df4fb90f1e
1 file changed