fix(cassandra): fix deseriazilation issue of cassandra repository (spark-jobserver#873)

* Fix deseriazilation issue of cassandra repository because order of retrieved bytes is wrong

Author: f1yegor

job-server/src/main/scala/spark/jobserver/io/JobCassandraDAO.scala

@@ -223,7 +223,7 @@ class JobCassandraDAO(config: Config) extends JobDAO with FileCacher {
     val tuples = JListWrapper(rows).toIndexedSeq.map { row =>
       (row.getInt(ChunkIndex), row.getBytes(Binary).array())
     }
-    tuples.sortBy(_._1).toMap.values.foldLeft(Array[Byte]()) { _ ++ _ }
+    tuples.map(_._2).foldLeft(Array[Byte]()) { _ ++ _ }
   }
 
   override def getJobInfo(jobId: String): Future[Option[JobInfo]] = {

job-server/src/test/scala/spark/jobserver/io/JobCassandraDAOSpec.scala

@@ -138,6 +138,7 @@ class JobCassandraDAOSpec extends TestJarFinder with FunSpecLike with Matchers w
       jarFilePath should equal (jarFile.getAbsolutePath)
       val retrieved = new File(jarFilePath)
       jarFile.length() should equal (retrieved.length())
+      Files.toByteArray(jarFile) should equal(Files.toByteArray(retrieved))
     }
 
     it("should retrieve the jar binary content for remote job manager") {
@@ -150,6 +151,7 @@ class JobCassandraDAOSpec extends TestJarFinder with FunSpecLike with Matchers w
       // test
       jarFile.exists() should equal (true)
       jarBinaryContent.length should equal (jarBytes.length)
+      jarBinaryContent should equal(jarBytes)
     }
   }