Increase DEFAULT_DATA_SIZE_PER_COLUMN value

Average row size for fixed width type is handled explicitly
therefore we can increase default row size to larger values
since it covers variable length types.

presto-main/src/main/java/com/facebook/presto/cost/PlanNodeStatsEstimate.java

@@ -35,7 +35,7 @@
 
 public class PlanNodeStatsEstimate
 {
-    private static final double DEFAULT_DATA_SIZE_PER_COLUMN = 10;
+    private static final double DEFAULT_DATA_SIZE_PER_COLUMN = 50;
     public static final PlanNodeStatsEstimate UNKNOWN_STATS = builder().build();
 
     private final double outputRowCount;