[REFACTOR] cleaned up checkVersion method in OSN

Removed the nested if/else branches.

Change-Id: I78a2db8018ba6d92b9f40c06152fc59a20118943
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1039
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>