[PreVerfiedDomains] use flattened string for get-domain-verification-agent

This way the result String can be directly used as an input using
ComponentName.unflattenFromString() in the tests.

BUG: 307327678
Test: manual with adb

Change-Id: I3642a9fab139211f99edefcd676ae88af2d86852
diff --git a/services/core/java/com/android/server/pm/PackageManagerShellCommand.java b/services/core/java/com/android/server/pm/PackageManagerShellCommand.java
index 89589ed..4fb9b56 100644
--- a/services/core/java/com/android/server/pm/PackageManagerShellCommand.java
+++ b/services/core/java/com/android/server/pm/PackageManagerShellCommand.java
@@ -4801,7 +4801,7 @@
         try {
             final ComponentName domainVerificationAgent = mInterface.getDomainVerificationAgent();
             pw.println(domainVerificationAgent == null
-                    ? "No Domain Verifier available!" : domainVerificationAgent.toString());
+                    ? "No Domain Verifier available!" : domainVerificationAgent.flattenToString());
         } catch (Exception e) {
             pw.println("Failure [" + e.getMessage() + "]");
             return 1;