[SC-5715] Workaround Scala 2.10 specific sql/core compilation error

## What changes were proposed in this pull request?

`DatabricksAtomicCommitProtocol.scala` doesn't compile under Scala 2.10 due to a Scala 2.10 compiler issue. This PR tries to workaround this issue.

## How was this patch tested?

N/A.

[1]: https://databricks.atlassian.net/browse/SC-5715

Author: Cheng Lian <lian@databricks.com>

Closes apache#191 from liancheng/workaround-fs-compilation-error.

sql/core/src/main/scala/com/databricks/sql/transaction/DatabricksAtomicCommitProtocol.scala

@@ -14,7 +14,7 @@ import java.nio.charset.StandardCharsets
 import scala.collection.mutable
 import scala.util.control.NonFatal
 
-import org.apache.hadoop.fs._
+import org.apache.hadoop.fs.{FileSystem => HadoopFileSystem, _}
 import org.apache.hadoop.mapreduce._
 import org.json4s.NoTypeHints
 import org.json4s.jackson.Serialization
@@ -79,7 +79,7 @@ class DatabricksAtomicCommitProtocol(jobId: String, path: String)
     finalPath.toString
   }
 
-  override def deleteWithJob(_fs: FileSystem, path: Path, recursive: Boolean): Boolean = {
+  override def deleteWithJob(_fs: HadoopFileSystem, path: Path, recursive: Boolean): Boolean = {
     val fs = testingFs.getOrElse(_fs)
     val sparkSession = SparkSession.getActiveSession.get
     if (!sparkSession.sqlContext.getConf(