Change discrete threshold value to string

For compliance with redfish schema, trigger with discrete
thresholds should use string as a value - instead of double.
This will impact dbus method "AddTrigger" for Trigger interface.
As there are currently no known sensors with discrete values,
telemetry service will still treat the value as a double internally.

Tested:
 - UT passed.
 - Trigger with discrete threshold value was successfully created
   using dbus call.
 - local redfish-tests for trigger persistency are passing after
   type modification.

Signed-off-by: Szymon Dompke <szymon.dompke@intel.com>
Change-Id: I8201ce5e2a45647206c5ccd85fc45ea8f32961af
diff --git a/tests/src/test_trigger_manager.cpp b/tests/src/test_trigger_manager.cpp
index 773b809..704c497 100644
--- a/tests/src/test_trigger_manager.cpp
+++ b/tests/src/test_trigger_manager.cpp
@@ -76,9 +76,9 @@
 {
     TriggerParams triggerParamsDiscrete;
     auto thresholds = std::vector<discrete::LabeledThresholdParam>{
-        {"discrete_threshold1", discrete::Severity::ok, 10, 11.0},
-        {"discrete_threshold2", discrete::Severity::warning, 10, 12.0},
-        {"discrete_threshold3", discrete::Severity::critical, 10, 13.0}};
+        {"discrete_threshold1", discrete::Severity::ok, 10, "11.0"},
+        {"discrete_threshold2", discrete::Severity::warning, 10, "12.0"},
+        {"discrete_threshold3", discrete::Severity::critical, 10, "13.0"}};
 
     triggerParamsDiscrete.thresholdParams(thresholds).isDiscrete(true);
 
@@ -230,8 +230,8 @@
 {
     LabeledTriggerThresholdParams thresholdParams =
         std::vector<discrete::LabeledThresholdParam>{
-            {"userId1", discrete::Severity::warning, 15, 10.0},
-            {"userId2", discrete::Severity::critical, 5, 20.0}};
+            {"userId1", discrete::Severity::warning, 15, "10.0"},
+            {"userId2", discrete::Severity::critical, 5, "20.0"}};
 
     data1["ThresholdParamsDiscriminator"] = thresholdParams.index();