Tests: clean DB after run in tests

Clean DB after each test run in BasicTests, MakerOnlyOrders,
MarketOrders, and LimitOrders test classes. This is needed for
all tests to start from empty state.

This commit exposes bug in end2end test - response to the first
LimitOrder should be None, not Some(Full). It will be fixed
later.

src/FX.Tests/BasicTests.cs

@@ -21,6 +21,12 @@ internal static void ClearRedisStorage()
             }
         }
 
+        [TearDown]
+        public void TearDown()
+        {
+            ClearRedisStorage();
+        }
+
         internal static IEnumerable<Exchange> CreateExchangesOfDifferentTypes()
         {
             yield return new Exchange(Persistence.Memory);

src/FX.Tests/LimitOrders.cs

@@ -13,6 +13,12 @@ namespace FsharpExchange.Tests
     [TestFixture]
     public class LimitOrders
     {
+        [TearDown]
+        public void TearDown()
+        {
+            BasicTests.ClearRedisStorage();
+        }
+
         internal static FSharpOption<Match> SendOrder(Exchange exchange,
                                        LimitOrder limitOrder,
                                        Market market)

src/FX.Tests/MakerOnlyOrders.cs

@@ -11,6 +11,12 @@ namespace FsharpExchange.Tests
     [TestFixture]
     public class MakerOnlyOrders
     {
+        [TearDown]
+        public void TearDown()
+        {
+            BasicTests.ClearRedisStorage();
+        }
+
         internal static IEnumerable<Exchange>
             Limit_order_is_accepted_by_empty_exchange
             (LimitOrder limitOrder,

src/FX.Tests/MarketOrders.cs

@@ -10,6 +10,12 @@ namespace FsharpExchange.Tests
     [TestFixture]
     public class MarketOrders
     {
+        [TearDown]
+        public void TearDown()
+        {
+            BasicTests.ClearRedisStorage();
+        }
+
         private void Market_order_exact_match_on_exchange_with_one_limit_order(Side side)
         {
             var quantity = 1;