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
iterator,
				levelDefs,
				false );
		IHierarchy hierarchy = dimensions[0].getHierarchy( );
		assertEquals( hierarchy.getName( ), "dimension1" );
		assertEquals( dimensions[0].length( ), 13 );
		
		levelNames = new String[]{
				"level21", "attr21"
		};
		iterator = new DimensionForTest( levelNames );
		iterator.setLevelMember( 0, distinct( TestFactTable.DIM1_L1Col ) );
		iterator.setLevelMember( 1, TestFactTable.ATTRIBUTE_Col );
		
		levelDefs = new ILevelDefn[1];
		levelDefs[0] = new LevelDefinition( "level21", new String[]{
			"level21"
		}, new String[]{
			"attr21"
		} );
		dimensions[1] = (Dimension) DimensionFactory.createDimension( "dimension2",
				documentManager,
				iterator,
				levelDefs,
				false );
		hierarchy = dimensions[1].getHierarchy( );
		assertEquals( hierarchy.getName( ), "dimension2" );
		assertEquals( dimensions[1].length( ), 5 );
		TestFactTable factTable2 = new TestFactTable( );
		String[] measureColumnName = new String[1];