Add callback support to triggerable actions

Change-Id: Icc27fbe9403eda418f41e12c76af7f3216f4b72a
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/bmc/firmware-handler/test/firmware_skip_unittest.cpp b/bmc/firmware-handler/test/firmware_skip_unittest.cpp
index a549582..243380d 100644
--- a/bmc/firmware-handler/test/firmware_skip_unittest.cpp
+++ b/bmc/firmware-handler/test/firmware_skip_unittest.cpp
@@ -13,7 +13,12 @@
 {
     SkipAction skip;
     EXPECT_TRUE(skip.trigger());
+    size_t i = 0;
+    skip.setCallback([&](TriggerableActionInterface&) { i++; });
     EXPECT_TRUE(skip.trigger());
+    EXPECT_EQ(1, i);
+    EXPECT_TRUE(skip.trigger());
+    EXPECT_EQ(2, i);
 }
 
 TEST(SkipActionTest, ValidateStatusAlwaysSuccess)