add tcp keep alive hack to net5 target (#560)

* add tcp keep alive hack to net5 target

* remove unused code

* fix ep

* Update buildtest.yaml

* fix netstandard21

* fix space

* fix net5 warning

* more comment

tests/KubernetesClient.Tests/AuthTests.cs

@@ -165,7 +165,7 @@ namespace k8s.Tests
             }
         }
 
-#if NETSTANDARD2_1 // The functionality under test, here, is dependent on managed HTTP / WebSocket in .NET Core 2.1 or newer.
+#if NETSTANDARD2_1 || NET5_0 // The functionality under test, here, is dependent on managed HTTP / WebSocket in .NET Core 2.1 or newer.
         // this test doesn't work on OSX and is inconsistent on windows
         [OperatingSystemDependentFact(Exclude = OperatingSystems.OSX | OperatingSystems.Windows)]
         public void Cert()
@@ -338,7 +338,7 @@ namespace k8s.Tests
                 }
             }
         }
-#endif // NETSTANDARD2_1
+#endif // NETSTANDARD2_1 || NET5_0
 
         [Fact]
         public void ExternalToken()

tests/KubernetesClient.Tests/KubernetesExecTests.cs

@@ -1,4 +1,4 @@
-#if !NETSTANDARD2_1
+#if !NETSTANDARD2_1 || NET5_0
 /*
  * These tests are only for the netstandard version of the client (there are separate tests for netcoreapp that connect to a local test-hosted server).
  */

tests/KubernetesClient.Tests/Mock/MockWebSocketBuilder.cs

@@ -1,4 +1,4 @@
-#if !NETSTANDARD2_1
+#if !NETSTANDARD2_1 || NET5_0
 using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
@@ -43,4 +43,4 @@ namespace k8s.Tests.Mock
     }
 }
 
-#endif // !NETSTANDARD2_1
+#endif // !NETSTANDARD2_1 || NET5_0