[SPARK-16909][SPARK CORE] Streaming for postgreSQL JDBC driver

As per the postgreSQL JDBC driver [implementation](https://github.com/pgjdbc/pgjdbc/blob/ab2a6d89081fc2c1fdb2a8600f413db33669022c/pgjdbc/src/main/java/org/postgresql/PGProperty.java#L99), the default record fetch size is 0(which means, it caches all record)

This fix enforces default record fetch size as 10 to enable streaming of data.

Author: Prince J Wesley <princejohnwesley@gmail.com>

Closes #14502 from princejwesley/spark-postgres.

core/src/main/scala/org/apache/spark/rdd/JdbcRDD.scala

@@ -79,14 +79,20 @@ class JdbcRDD[T: ClassTag](
     val conn = getConnection()
     val stmt = conn.prepareStatement(sql, ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY)
 
-    // setFetchSize(Integer.MIN_VALUE) is a mysql driver specific way to force streaming results,
-    // rather than pulling entire resultset into memory.
-    // see http://dev.mysql.com/doc/refman/5.0/en/connector-j-reference-implementation-notes.html
-    if (conn.getMetaData.getURL.matches("jdbc:mysql:.*")) {
+    val url = conn.getMetaData.getURL
+    if (url.startsWith("jdbc:mysql:")) {
+      // setFetchSize(Integer.MIN_VALUE) is a mysql driver specific way to force
+      // streaming results, rather than pulling entire resultset into memory.
+      // See the below URL
+      // dev.mysql.com/doc/connector-j/5.1/en/connector-j-reference-implementation-notes.html
+
       stmt.setFetchSize(Integer.MIN_VALUE)
-      logInfo("statement fetch size set to: " + stmt.getFetchSize + " to force MySQL streaming ")
+    } else {
+      stmt.setFetchSize(100)
     }
 
+    logInfo(s"statement fetch size set to: ${stmt.getFetchSize}")
+
     stmt.setLong(1, part.lower)
     stmt.setLong(2, part.upper)
     val rs = stmt.executeQuery()