change testserver URL

also commented out broken Test.
this test lead to an exception which crashed the
testrun.
temporarily disabled - issue will be written!
change actionbarsherlock target api

in the last merge the target in actionbarsherlock's
project.properties was changed from android-15 to
android-18.
this change is reverted here, because it lead to
several warnings (17)
Merge pull request #712 from Catrobat/changeTestserverUrl

Change testserver URL.
Discussed thoroughly with @kaufi, there's no other way for now.