Fixes to the QueryBugsTest (#162)

* Ensure connection is closed before dropping the database/deleting the file

* Upgrade the QueryBugsTest

test/EFCore.Jet.FunctionalTests/TestUtilities/JetTestHelpers.cs

@@ -9,7 +9,7 @@ using Microsoft.Extensions.DependencyInjection;
 
 namespace EntityFrameworkCore.Jet.FunctionalTests.TestUtilities
 {
-    public class JetTestHelpers : TestHelpers
+    public class JetTestHelpers : RelationalTestHelpers
     {
         protected JetTestHelpers()
         {

test/EFCore.Jet.FunctionalTests/TestUtilities/JetTestStore.cs

@@ -159,7 +159,13 @@ namespace EntityFrameworkCore.Jet.FunctionalTests.TestUtilities
         }
 
         public void DeleteDatabase()
-            => JetConnection.DropDatabase(CreateConnectionString(Name));
+        {
+            if (ConnectionState != ConnectionState.Closed)
+            {
+                CloseConnection();
+            }
+            JetConnection.DropDatabase(CreateConnectionString(Name));
+        }
 
         public override void OpenConnection()
             => new TestJetRetryingExecutionStrategy().Execute(Connection, connection => connection.Open());