Rename apex keys to match with APEX bundle name

This is to ensure that an apex key is used by only one APEX.

Bug: 115721587
Test: m checkbuild
Change-Id: Id89fe87f91aa571730c3748e7b03f3b71cdcf501
diff --git a/apex/Android.bp b/apex/Android.bp
index bb73ead..575603f 100644
--- a/apex/Android.bp
+++ b/apex/Android.bp
@@ -35,6 +35,6 @@
 
 apex_key {
     name: "com.android.media.key",
-    public_key: "media.avbpubkey",
-    private_key: "media.pem",
+    public_key: "com.android.media.avbpubkey",
+    private_key: "com.android.media.pem",
 }