Add more enums to the ota type

We'd better have a default type for enums. It's safe to change the
proto definition now since no one is parsing the new meta.

Also add the brick type for manually generated brick pkgs.

Bug: 166154730
Test: unit tests pass
Change-Id: Ie6d4e695c298313276b559601509c9a7a7ee91b1

tools/releasetools/ota_metadata.proto

@@ -64,8 +64,10 @@ message DeviceState {
 // and prerequisite to install the update correctly.
 message OtaMetadata {
   enum OtaType {
-    AB = 0;
-    BLOCK = 1;
+    UNKNOWN = 0;
+    AB = 1;
+    BLOCK = 2;
+    BRICK = 3;
   };
   OtaType type = 1;
   // True if we need to wipe after the update.