Upgrade to golang protobuf api v2

Major operations:
 * Fix the go_package entries to be consistent, as the new tool
   complains when it doesn't have a '/'.
 * Regenerate with the new protoc-gen-go tool.
 * github.com/golang/protobuf -> google.golang.org/protobuf
 * proto.[Un]MarshalText -> prototext.[Un]Marshal

Change-Id: Ie1147bd2457fafb66ba555461b3bf14f0561a25d
diff --git a/tests/lib.sh b/tests/lib.sh
index f1e1efa..1d9b8d4 100644
--- a/tests/lib.sh
+++ b/tests/lib.sh
@@ -86,6 +86,7 @@
 
   symlink_directory prebuilts/go
   symlink_directory prebuilts/build-tools
+  symlink_directory external/go-cmp
   symlink_directory external/golang-protobuf
 
   touch "$MOCK_TOP/Android.bp"