[trusty][apploader] Handle APPLOADER_ERR_POLICY_VIOLATION

Add a specific error message to the Android CLI tool for the
case where the policy engine (http://go/aog/2051516) disallows
loading.

Test: Load a signed app that violates the policy
Bug: 208968719
Change-Id: I2aaa218ab3a7297ea62448de49baa0bfd6b1ee52
diff --git a/trusty/apploader/apploader.cpp b/trusty/apploader/apploader.cpp
index c72af40..278499f 100644
--- a/trusty/apploader/apploader.cpp
+++ b/trusty/apploader/apploader.cpp
@@ -223,6 +223,9 @@
         case APPLOADER_ERR_INVALID_VERSION:
             LOG(ERROR) << "Error: invalid application version";
             break;
+        case APPLOADER_ERR_POLICY_VIOLATION:
+            LOG(ERROR) << "Error: loading denied by policy engine";
+            break;
         default:
             LOG(ERROR) << "Unrecognized error: " << resp.error;
             break;