Fix for save as Json failure (#216)

* Fix exception due to repeat disposal of stream

* Fix off by one index for saving selection

* Fix to overwrite file if file already exists

* Fix test for Json save selection

* Add Json Formatting

test/Microsoft.SqlTools.ServiceLayer.Test/QueryExecution/DataStorage/SaveAsJsonFileStreamWriterTests.cs

@@ -95,7 +95,7 @@ namespace Microsoft.SqlTools.ServiceLayer.Test.QueryExecution.DataStorage
             var saveParams = new SaveResultsAsJsonRequestParams
             {
                 ColumnStartIndex = 1,
-                ColumnEndIndex = 3,
+                ColumnEndIndex = 2,
                 RowStartIndex = 0,          // Including b/c it is required to be a "save selection"
                 RowEndIndex = 10
             };