Bug 182895 Support sort on Level attribute.
Currently in OLAP engine we only support sort on level key value. We should go ahead to support sort on level attribute value.
data/org.eclipse.birt.data.tests/test/org/eclipse/birt/data/engine/olap/api/CubeFeaturesTest.java
CubeSortDefinition sorter1 = new CubeSortDefinition();
		sorter1.setExpression( "data[\"rowGrandTotal\"]" );
		sorter1.setAxisQualifierLevels( null );
		sorter1.setAxisQualifierValues( null );
		sorter1.setTargetLevel( level21 );
		sorter1.setSortDirection( ISortDefinition.SORT_DESC );
		
		
		CubeSortDefinition sorter2 = new CubeSortDefinition();
		sorter2.setExpression( "data[\"city_year_total\"]" );
		sorter2.setAxisQualifierLevels( new ILevelDefinition[]{level21} );
		sorter2.setAxisQualifierValues( new Object[]{"2002"} );
		sorter2.setTargetLevel( level12 );
		sorter2.setSortDirection( ISortDefinition.SORT_DESC );
		
		CubeSortDefinition sorter3 = new CubeSortDefinition();
		sorter3.setExpression( "data[\"country_year_total\"]" );
		sorter3.setAxisQualifierLevels( new ILevelDefinition[]{level21} );
		sorter3.setAxisQualifierValues( new Object[]{"2002"} );
		sorter3.setTargetLevel( level11 );
		sorter3.setSortDirection( ISortDefinition.SORT_DESC );
		
		CubeSortDefinition sorter4 = new CubeSortDefinition();
		sorter4.setExpression( "dimension[\"dimension1\"][\"level13\"]" );
		sorter4.setAxisQualifierLevels( null );
		sorter4.setAxisQualifierValues( null );
		sorter4.setTargetLevel( level13 );
		sorter4.setSortDirection( ISortDefinition.SORT_DESC );