Do not rely on $HOME since it can be too long, use /tmp (#27853)

Author: Paulo Janotti

src/System.IO.Pipes/tests/NamedPipeTests/NamedPipeTest.UnixDomainSockets.cs

@@ -14,8 +14,7 @@ public class NamedPipeTest_UnixDomainSockets : NamedPipeTestBase
         [PlatformSpecific(TestPlatforms.AnyUnix)]
         public void NamedPipeServer_Connects_With_UnixDomainSocketEndPointClient()
         {
-            string absoluteHomePath = Path.GetFullPath(Environment.GetEnvironmentVariable("HOME"));
-            string pipeName = Path.Combine(absoluteHomePath, "pipe-tests-corefx-" + Path.GetRandomFileName());
+            string pipeName = Path.Combine("/tmp", "pipe-tests-corefx-" + Path.GetRandomFileName());
             var endPoint = new UnixDomainSocketEndPoint(pipeName);
 
             using (var pipeServer = new NamedPipeServerStream(pipeName, PipeDirection.InOut, 1, PipeTransmissionMode.Byte, PipeOptions.CurrentUserOnly))
@@ -32,8 +31,7 @@ public void NamedPipeServer_Connects_With_UnixDomainSocketEndPointClient()
         [PlatformSpecific(TestPlatforms.AnyUnix)]
         public async Task NamedPipeClient_Connects_With_UnixDomainSocketEndPointServer()
         {
-            string absoluteHomePath = Path.GetFullPath(Environment.GetEnvironmentVariable("HOME"));
-            string pipeName = Path.Combine(absoluteHomePath, "pipe-tests-corefx-" + Path.GetRandomFileName());
+            string pipeName = Path.Combine("/tmp", "pipe-tests-corefx-" + Path.GetRandomFileName());
             var endPoint = new UnixDomainSocketEndPoint(pipeName);
 
             using (var socketServer = new Socket(AddressFamily.Unix, SocketType.Stream, ProtocolType.Unspecified))