[SPARK-24829][STS] In Spark Thrift Server, CAST AS FLOAT inconsistent with spark-shell or spark-sql

## What changes were proposed in this pull request?

SELECT CAST('4.56' AS FLOAT)

the result is 4.559999942779541

![2018-07-18_110944](https://user-images.githubusercontent.com/24823338/42857199-7c6783da-8a7b-11e8-8c69-1e9302102525.png)

 it should be 4.56 as same as in spark-shell or spark-sql.

![2018-07-18_111111](https://user-images.githubusercontent.com/24823338/42857210-80c89e96-8a7b-11e8-9f8c-de1a79a73752.png)

## How was this patch tested?

add unit tests

Author: zuotingbing <[email protected]>

Closes apache#21789 from zuotingbing/SPARK-24829.

Author: zuotingbing

sql/hive-thriftserver/src/main/java/org/apache/hive/service/cli/Column.java

@@ -349,7 +349,7 @@ public void addValue(Type type, Object field) {
         break;
       case FLOAT_TYPE:
         nulls.set(size, field == null);
-        doubleVars()[size] = field == null ? 0 : ((Float)field).doubleValue();
+        doubleVars()[size] = field == null ? 0 : new Double(field.toString());
         break;
       case DOUBLE_TYPE:
         nulls.set(size, field == null);

sql/hive-thriftserver/src/test/scala/org/apache/spark/sql/hive/thriftserver/HiveThriftServer2Suites.scala

@@ -636,6 +636,14 @@ class HiveThriftBinaryServerSuite extends HiveThriftJdbcTest {
       assert(pipeoutFileList(sessionID).length == 0)
     }
   }
+
+  test("SPARK-24829 Checks cast as float") {
+    withJdbcStatement() { statement =>
+      val resultSet = statement.executeQuery("SELECT CAST('4.56' AS FLOAT)")
+      resultSet.next()
+      assert(resultSet.getString(1) === "4.56")
+    }
+  }
 }
 
 class SingleSessionSuite extends HiveThriftJdbcTest {
@@ -766,6 +774,14 @@ class HiveThriftHttpServerSuite extends HiveThriftJdbcTest {
       assert(resultSet.getString(2) === HiveUtils.builtinHiveVersion)
     }
   }
+
+  test("SPARK-24829 Checks cast as float") {
+    withJdbcStatement() { statement =>
+      val resultSet = statement.executeQuery("SELECT CAST('4.56' AS FLOAT)")
+      resultSet.next()
+      assert(resultSet.getString(1) === "4.56")
+    }
+  }
 }
 
 object ServerMode extends Enumeration {