fix failing testcase

one build in our multi-job failed but is working in single runs.
https://jenkins.catrob.at/job/Catroid-Multi-Job/134/testReport/org.catrobat.catroid.uitest.ui.activity/ScriptActivityTest/testActionBarTitle/history/?

test was refactored - a green build is possible ^^
testrun: https://jenkins.catrob.at/job/Catroid-Multi-Job-Custom-Branch/319/ 

I also refactored the testBackgroundSprite; this testcase created projects with a custom name: a prefix ("something") and a timestamp, but these projects are not deleted. good practise is to use programnames from UiTestUtils if possible, because programs with these names are handled by the tearDown of the basetestclass.