fixed clients overlapping from one test to another by:

- adding client and server wrappers to verify the clientid starts with the testname
- adding disposable baseclass
- clear disconnect handler from client so it does not try to reconnect after it is disposed
- moved code from dispose to cleanup in case it is called in a stop method as dispose may only be called once while start / stop may be called multiple times

Tests/MQTTnet.Core.Tests/RPC_Tests.cs

@@ -18,6 +18,8 @@ namespace MQTTnet.Tests
     [TestClass]
     public class RPC_Tests
     {
+        public TestContext TestContext { get; set; }
+
         [TestMethod]
         public Task Execute_Success_With_QoS_0()
         {
@@ -58,7 +60,7 @@ namespace MQTTnet.Tests
         [ExpectedException(typeof(MqttCommunicationTimedOutException))]
         public async Task Execute_Timeout()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
                 
@@ -73,7 +75,7 @@ namespace MQTTnet.Tests
         [ExpectedException(typeof(MqttCommunicationTimedOutException))]
         public async Task Execute_With_Custom_Topic_Names()
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
 
@@ -86,7 +88,7 @@ namespace MQTTnet.Tests
 
         private async Task Execute_Success(MqttQualityOfServiceLevel qosLevel, MqttProtocolVersion protocolVersion)
         {
-            using (var testEnvironment = new TestEnvironment())
+            using (var testEnvironment = new TestEnvironment(TestContext))
             {
                 await testEnvironment.StartServerAsync();
                 var responseSender = await testEnvironment.ConnectClientAsync(new MqttClientOptionsBuilder().WithProtocolVersion(protocolVersion));