[LMS-2104] fixed broken DataSetDownloadServlet tests;

...stemsx/cisd/etlserver/postregistration/NotifyingTask.java

...sd/openbis/dss/generic/server/DatasetDownloadServlet.java

...enbis/dss/generic/shared/HierarchicalContentProvider.java

...nbis/dss/generic/shared/IHierarchicalContentProvider.java

...openbis/dss/generic/shared/utils/DatasetLocationUtil.java

...openbis/dss/generic/shared/utils/SegmentedStoreUtils.java

...penbis/dss/generic/server/DatasetDownloadServletTest.java

...server/plugins/standard/MockDataSetDirectoryProvider.java

...s/dss/generic/shared/HierarchicalContentProviderTest.java

...a/ch/systemsx/cisd/openbis/generic/server/ETLService.java

...er/dataaccess/DataStoreServerBasedDataSourceProvider.java