Keystore 2.0: Implement clear namespace.

Implements the clearing of a specific namespace. This is requered for
uninstalling an app.

Test: Uninstall an app and check that all its keys get deleted.
Bug: 176123105
Change-Id: I519519f9381ee70a3dd2a93d77db92a510aa8427
diff --git a/keystore2/aidl/Android.bp b/keystore2/aidl/Android.bp
index d529fa9..c92417b 100644
--- a/keystore2/aidl/Android.bp
+++ b/keystore2/aidl/Android.bp
@@ -118,6 +118,9 @@
 aidl_interface {
     name: "android.security.usermanager",
     srcs: [ "android/security/usermanager/*.aidl" ],
+    imports: [
+        "android.system.keystore2",
+    ],
     unstable: true,
     backend: {
         java: {