Fix Bazel build with testonly attribute set

Replication plugin tests depend on //gerrit-acceptance-framework:lib
which is flagged with testonly attribute.

For Bazel, all the dependencies in the tree need to have the testonly
set consistently.

Change-Id: I0eb3f6c3f2123b66b98b8c8060badc9bbaa88dd6
diff --git a/BUILD b/BUILD
index eeabb9d..097d258 100644
--- a/BUILD
+++ b/BUILD
@@ -39,4 +39,5 @@
     '//gerrit-acceptance-framework:lib',
     '//gerrit-plugin-api:lib',
   ],
+  testonly = 1,
 )