Handle errors listing flavors and images in scenario utils

This commit adds a try except block around the api calls made during
the scenario tests' testscenario utils module. This is needed because
if a config file is present but has incorrect information the errors
raised will cause import failures during discovery. This will cause
test list (or any other operation which involves test discovery) to
fail.

Change-Id: I8f31abcba547be78fc2dc9250f522bb6ac14cb01
Closes-Bug: #1405797
1 file changed