DPL: avoid ODC waiting indefinitely for the driver

When deploying in embedded mode, ODC will wait for the driver
to transition through the state machine stetes. However right
now the driver itself is not a FairMQ device, nor has any special
plugin, so Control will wait for a transition which will never happen
and eventually kill the run.

This marks the task as expendable, telling ODC to ignore the state
changes for it, hopefully working around the problem.

Being expendable is also probably a good idea, because we do not want
that a bug in the GUI crashes the whole workflow.

Framework/Core/src/DDSConfigHelpers.cxx

@@ -135,7 +135,7 @@ void DDSConfigHelpers::dumpDeviceSpec2DDS(std::ostream& out,
   }
   out << R"(<topology name="o2-dataflow">)"
          "\n";
-  if (hasExpendableTask) {
+  if (hasExpendableTask || driverMode == DriverMode::EMBEDDED) {
     out << R"(<declrequirement name="odc_expendable_task" type="custom" value="true" />)"
            "\n";
   }
@@ -180,6 +180,9 @@ void DDSConfigHelpers::dumpDeviceSpec2DDS(std::ostream& out,
         << R"(<exe reachable="true">)";
     out << fmt::format("cat ${{DDS_LOCATION}}/dpl_json{}.asset | o2-dpl-run --driver-mode embedded", workflowSuffix);
     out << R"(</exe>)"
+        << "<requirements>\n"
+        << "  <requirement name=\"odc_expendable_task\" />\n"
+        << "</requirements>\n"
         << "\n";
     out << "</decltask>";
   }