all: Add grpc-xds

This will fix reporting of xDS code coverage.
diff --git a/all/build.gradle b/all/build.gradle
index fad1a17..ab8cf8b 100644
--- a/all/build.gradle
+++ b/all/build.gradle
@@ -18,6 +18,7 @@
     project(':grpc-protobuf-lite'),
     project(':grpc-stub'),
     project(':grpc-testing'),
+    project(':grpc-xds'),
 ]
 
 for (subproject in rootProject.subprojects) {