Address review comments from @tdas

* add test which restores query from Spark 2.3.1

Author: HeartSaVioR

sql/core/src/test/resources/structured-streaming/checkpoint-version-2.3.1-streaming-aggregate-state-format-1/commits/0

@@ -0,0 +1,2 @@
+v1
+{}

sql/core/src/test/resources/structured-streaming/checkpoint-version-2.3.1-streaming-aggregate-state-format-1/commits/1

@@ -0,0 +1,2 @@
+v1
+{}

sql/core/src/test/resources/structured-streaming/checkpoint-version-2.3.1-streaming-aggregate-state-format-1/metadata

@@ -0,0 +1 @@
+{"id":"2f32aca2-1b97-458f-a48f-109328724f09"}

sql/core/src/test/resources/structured-streaming/checkpoint-version-2.3.1-streaming-aggregate-state-format-1/offsets/0

@@ -0,0 +1,3 @@
+v1
+{"batchWatermarkMs":0,"batchTimestampMs":1533784347136,"conf":{"spark.sql.shuffle.partitions":"5","spark.sql.streaming.stateStore.providerClass":"org.apache.spark.sql.execution.streaming.state.HDFSBackedStateStoreProvider"}}
+0

sql/core/src/test/resources/structured-streaming/checkpoint-version-2.3.1-streaming-aggregate-state-format-1/offsets/1

@@ -0,0 +1,3 @@
+v1
+{"batchWatermarkMs":0,"batchTimestampMs":1533784349160,"conf":{"spark.sql.shuffle.partitions":"5","spark.sql.streaming.stateStore.providerClass":"org.apache.spark.sql.execution.streaming.state.HDFSBackedStateStoreProvider"}}
+1