[SPARK-18141][SQL] Fix to quote column names in the predicate clause …

…of the JDBC RDD generated sql statement

## What changes were proposed in this pull request?

SQL query generated for the JDBC data source is not quoting columns in the predicate clause. When the source table has quoted column names,  spark jdbc read fails with column not found error incorrectly.

Error:
org.h2.jdbc.JdbcSQLException: Column "ID" not found;
Source SQL statement:
SELECT "Name","Id" FROM TEST."mixedCaseCols" WHERE (Id < 1)

This PR fixes by quoting column names in the generated  SQL for predicate clause  when filters are pushed down to the data source.

Source SQL statement after the fix:
SELECT "Name","Id" FROM TEST."mixedCaseCols" WHERE ("Id" < 1)

## How was this patch tested?

Added new test case to the JdbcSuite

Author: sureshthalamati <suresh.thalamati@gmail.com>

Closes apache#15662 from sureshthalamati/filter_quoted_cols-SPARK-18141.

sql/core/src/test/scala/org/apache/spark/sql/jdbc/JDBCSuite.scala

@@ -210,6 +210,21 @@ class JDBCSuite extends SparkFunSuite
     conn.prepareStatement("""insert into test."mixedCaseCols" values (null, 3)""").executeUpdate()
     conn.commit()
 
+    sql(
+      s"""
+         |CREATE TEMPORARY TABLE mixedCaseCols
+         |USING org.apache.spark.sql.jdbc
+         |OPTIONS (url '$url', dbtable 'TEST."mixedCaseCols"', user 'testUser', password 'testPass')
+      """.stripMargin.replaceAll("\n", " "))
+
+    conn.prepareStatement(
+      """create table test."mixedCaseCols" ("Name" TEXT(32), "Id" INTEGER NOT NULL)""")
+      .executeUpdate()
+    conn.prepareStatement("""insert into test."mixedCaseCols" values ('fred', 1)""").executeUpdate()
+    conn.prepareStatement("""insert into test."mixedCaseCols" values ('mary', 2)""").executeUpdate()
+    conn.prepareStatement("""insert into test."mixedCaseCols" values (null, 3)""").executeUpdate()
+    conn.commit()
+
     sql(
       s"""
          |CREATE TEMPORARY TABLE mixedCaseCols