SceneGadgetTest : Extend idle wait for `testExpansion()`
SceneGadgetTest : Extend idle wait for `testExpansion()`

This seems to be enough to prevent failure on my machine - let's see what happens on Travis.

appleseedhq/gaffer,ivanimanishi/gaffer,andrewkaufman/gaffer,ivanimanishi/gaffer,GafferHQ/gaffer,andrewkaufman/gaffer,andrewkaufman/gaffer,hradec/gaffer,lucienfostier/gaffer,johnhaddon/gaffer,ivanimanishi/gaffer,ivanimanishi/gaffer,appleseedhq/gaffer,GafferHQ/gaffer,ImageEngine/gaffer,lucienfostier/gaffer,hradec/gaffer,GafferHQ/gaffer,johnhaddon/gaffer,GafferHQ/gaffer,boberfly/gaffer,ImageEngine/gaffer,hradec/gaffer,hradec/gaffer,appleseedhq/gaffer,boberfly/gaffer,lucienfostier/gaffer,johnhaddon/gaffer,ImageEngine/gaffer,hradec/gaffer,boberfly/gaffer,boberfly/gaffer,GafferHQ/gaffer,andrewkaufman/gaffer,lucienfostier/gaffer,ImageEngine/gaffer,johnhaddon/gaffer,andrewkaufman/gaffer,johnhaddon/gaffer,appleseedhq/gaffer