fix flaky Connectivity Tests (#1403)

these two tests were not waiting for the interruption (all other usages
of BreakConnections() did). This could cause random failures because
e.g. the wrong exception is thrown.

example: https://ci.appveyor.com/project/drieseng/ssh-net/builds/49831433/job/4urb0upx63bvxcgu

Co-authored-by: Rob Hague <rob.hague00@gmail.com>

Author: mus65

test/Renci.SshNet.IntegrationTests/ConnectivityTests.cs

@@ -171,6 +171,7 @@ public void Common_DetectConnectionResetThroughSftpInvocation()
 
                 try
                 {
+                    WaitForConnectionInterruption(client);
                     client.ListDirectory("/");
                     Assert.Fail();
                 }
@@ -260,9 +261,9 @@ public void Common_DetectLossOfNetworkConnectivityThroughSftpInvocation()
                 client.Connect();
 
                 var disruptor = _sshConnectionDisruptor.BreakConnections();
-                Thread.Sleep(100);
                 try
                 {
+                    WaitForConnectionInterruption(client);
                     client.ListDirectory("/");
                     Assert.Fail();
                 }