Split insert() into insert() & bulkInsert() (#69)

- Behaviour change for existing insert() users
 - Made the current insert() implementation, as something to use for bulkInsert()
 - Normal inserts now share a lot of code with upsert, which provides benefits like small file handling
 - Refactored/Cleaned up code in HoodieWriteClient for reuse
 - Added a unit test, switching few tests to call bulkInsert() and few to call insert()

hoodie-client/src/main/java/com/uber/hoodie/func/BulkInsertMapFunction.java

@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2016 Uber Technologies, Inc. (hoodie-dev-group@uber.com)
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *          http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.uber.hoodie.func;
+
+import com.uber.hoodie.config.HoodieWriteConfig;
+import com.uber.hoodie.WriteStatus;
+import com.uber.hoodie.common.model.HoodieRecord;
+import com.uber.hoodie.common.model.HoodieRecordPayload;
+import com.uber.hoodie.common.model.HoodieTableMetadata;
+import org.apache.spark.api.java.function.Function2;
+
+import java.util.Iterator;
+import java.util.List;
+
+
+/**
+ * Map function that handles a sorted stream of HoodieRecords
+ */
+public class BulkInsertMapFunction<T extends HoodieRecordPayload>
+    implements Function2<Integer, Iterator<HoodieRecord<T>>, Iterator<List<WriteStatus>>> {
+
+    private String commitTime;
+    private HoodieWriteConfig config;
+    private HoodieTableMetadata metadata;
+
+    public BulkInsertMapFunction(String commitTime, HoodieWriteConfig config,
+                                 HoodieTableMetadata metadata) {
+        this.commitTime = commitTime;
+        this.config = config;
+        this.metadata = metadata;
+    }
+
+    @Override
+    public Iterator<List<WriteStatus>> call(Integer partition, Iterator<HoodieRecord<T>> sortedRecordItr)
+        throws Exception {
+        return new LazyInsertIterable<>(sortedRecordItr, config, commitTime, metadata);
+    }
+}