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: I77ce1e20024fba382cfc07d22ef525f778804de6
diff --git a/build/apex/Android.bp b/build/apex/Android.bp
index bfaacb1..159e5c1 100644
--- a/build/apex/Android.bp
+++ b/build/apex/Android.bp
@@ -68,8 +68,8 @@
 
 apex_key {
     name: "com.android.runtime.key",
-    public_key: "runtime.avbpubkey",
-    private_key: "runtime.pem",
+    public_key: "com.android.runtime.avbpubkey",
+    private_key: "com.android.runtime.pem",
 }
 
 // TODO: Introduce `apex_defaults` to factor common parts of `apex`