Make apex.updatable default to true.

Update tests accordingly and add a new test case for this.

Bug: 180375550
Test: Treehugger
Change-Id: I835e189f4dae1e4bc79dce7bc59b7b9c7bd19fd9
diff --git a/apex/vndk_test.go b/apex/vndk_test.go
index 74a79e1..5e9a11f 100644
--- a/apex/vndk_test.go
+++ b/apex/vndk_test.go
@@ -13,6 +13,7 @@
 		apex_vndk {
 			name: "com.android.vndk.current",
 			key: "com.android.vndk.current.key",
+			updatable: false,
 		}
 
 		apex_key {
@@ -69,6 +70,7 @@
 		apex_vndk {
 			name: "com.android.vndk.current",
 			key: "mykey",
+			updatable: false,
 		}
 		apex_key {
 			name: "mykey",