make testAssetCatalog work on OS X 10.10

Change-Id: I79cdd19de11277d33852c4fb2b241a874148e775
Reviewed-by: Jake Petroules <jake.petroules@petroules.com>
fix iconset tests on OS X 10.10

The iconutil tool doesn't output warning messages about missing files
anymore. Also, there's no reason to test the behavior of this tool.

Change-Id: Ic0a6b7c0d4b524d2a70b9aac133ed084b4ee2a51
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
Reviewed-by: Jake Petroules <jake.petroules@petroules.com>