Introducing HoodieLogFormat V2 with versioning support

- HoodieLogFormat V2 has support for LogFormat evolution through versioning
			- LogVersion is associated with a LogBlock not a LogFile
			- Based on a version for a LogBlock, approporiate code path is executed
		- Implemented LazyReading of Hoodie Log Blocks with Memory / IO tradeoff
		- Implemented Reverse pointer to be able to traverse the log in reverse
		- Introduce new MAGIC for backwards compatibility with logs without versions

hoodie-common/src/test/java/com/uber/hoodie/common/model/HoodieTestUtils.java

@@ -291,8 +291,9 @@ public class HoodieTestUtils {
             .overBaseCommit(location.getCommitTime())
             .withFs(fs).build();
 
-        Map<HoodieLogBlock.LogMetadataType, String> metadata = Maps.newHashMap();
-        metadata.put(HoodieLogBlock.LogMetadataType.INSTANT_TIME, location.getCommitTime());
+        Map<HoodieLogBlock.HeaderMetadataType, String> header = Maps.newHashMap();
+        header.put(HoodieLogBlock.HeaderMetadataType.INSTANT_TIME, location.getCommitTime());
+        header.put(HoodieLogBlock.HeaderMetadataType.SCHEMA, schema.toString());
         logWriter.appendBlock(new HoodieAvroDataBlock(s.getValue().stream().map(r -> {
           try {
             GenericRecord val = (GenericRecord) r.getData().getInsertValue(schema).get();
@@ -304,7 +305,7 @@ public class HoodieTestUtils {
           } catch (IOException e) {
             return null;
           }
-        }).collect(Collectors.toList()), schema, metadata));
+        }).collect(Collectors.toList()), header));
         logWriter.close();
       } catch (Exception e) {
         fail(e.toString());