Add ability to show "installing security update"

Add a new command "--security" to boot commands. If this command is
observed as part of BCB, choose a different background text picture
for installing stage in recovery UI. As a result, users will see
"installing security update" instead of "installing system update"
when applying a security update package.

Bug: 27837319
Change-Id: I2e2253a124993ecc24804fa1ee0b918ac96837c5
diff --git a/tests/component/verifier_test.cpp b/tests/component/verifier_test.cpp
index 9ac9657..780ff28 100644
--- a/tests/component/verifier_test.cpp
+++ b/tests/component/verifier_test.cpp
@@ -46,6 +46,7 @@
     void SetStage(int, int) { }
     void SetLocale(const char*) { }
     void SetBackground(Icon icon) { }
+    void SetSystemUpdateText(bool security_update) { }
 
     void SetProgressType(ProgressType determinate) { }
     void ShowProgress(float portion, float seconds) { }