manager: led priority is optional

The default priority was "Blink" but now the priority is optional.

This helps to implement group priority.
So if someone wants to use group priority they can do so, without the
default led priority getting in the way.

The led priority can still be assigned as "Blink" explicitly if needed.

Change-Id: I9336487bcc2edc0b3308ee76eb5330b8222b7f25
Signed-off-by: Alexander Hansen <alexander.hansen@9elements.com>
diff --git a/test/utest-led-json.cpp b/test/utest-led-json.cpp
index 36eb404..afd4505 100644
--- a/test/utest-led-json.cpp
+++ b/test/utest-led-json.cpp
@@ -26,7 +26,7 @@
         ASSERT_EQ(group.action, phosphor::led::Layout::Action::On);
         ASSERT_EQ(group.dutyOn, 50);
         ASSERT_EQ(group.period, 0);
-        ASSERT_EQ(group.priority, phosphor::led::Layout::Action::Blink);
+        ASSERT_EQ(group.priority, std::nullopt);
     }
 
     for (const auto& group : powerOnActions)
@@ -45,14 +45,14 @@
             ASSERT_EQ(group.action, phosphor::led::Layout::Action::Blink);
             ASSERT_EQ(group.dutyOn, 50);
             ASSERT_EQ(group.period, 1000);
-            ASSERT_EQ(group.priority, phosphor::led::Layout::Action::Blink);
+            ASSERT_EQ(group.priority, std::nullopt);
         }
         else if (group.name == "rear_id")
         {
             ASSERT_EQ(group.action, phosphor::led::Layout::Action::Blink);
             ASSERT_EQ(group.dutyOn, 50);
             ASSERT_EQ(group.period, 1000);
-            ASSERT_EQ(group.priority, phosphor::led::Layout::Action::Blink);
+            ASSERT_EQ(group.priority, std::nullopt);
         }
         else
         {