use sockets:// instead of tcp://

sockets is expected to work on linux/mac, unlike tcp:// which only works
on linux right now.

Remoting/ServerManager/vtkPVCoreApplication.cxx

@@ -338,7 +338,7 @@ vtkSmartPointer<vtkPVApplicationOptions> vtkPVCoreApplication::CreateOptions() c
 //----------------------------------------------------------------------------
 std::string vtkPVCoreApplication::GetEngineURL() const
 {
-  return "tcp://";
+  return "sockets://";
 }
 
 //-----------------------------------------------------------------------------

Remoting/ServerManager/vtkPVServerApplication.cxx

@@ -78,8 +78,7 @@ std::string vtkPVServerApplication::GetEngineURL() const
 {
   auto* options = this->GetOptions();
   // FIXME: this doesn't work as expected.
-  // return fmt::format("tcp://{}:{}", options->GetLocalHostname(), options->GetPort());
-  return this->Superclass::GetEngineURL();
+  return fmt::format("sockets://{}:{}", options->GetLocalHostname(), options->GetPort());
 }
 
 //----------------------------------------------------------------------------