Expose WorkQueue constructor to pass in thread count

This allows me to bind the WorkQueue more explicitly in a vhost setup
like used on gerrit-review or the proposed gerrit-vhost library.

Change-Id: I7eeb38bae4368a03880d797aad131f7fb02a23bb
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/git/WorkQueue.java b/gerrit-server/src/main/java/com/google/gerrit/server/git/WorkQueue.java
index 6e274a1..60eacb1 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/git/WorkQueue.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/git/WorkQueue.java
@@ -90,10 +90,14 @@
   private final CopyOnWriteArrayList<Executor> queues;
 
   @Inject
-  WorkQueue(final IdGenerator idGenerator, @GerritServerConfig final Config cfg) {
+  WorkQueue(IdGenerator idGenerator, @GerritServerConfig Config cfg) {
+    this(idGenerator, cfg.getInt("execution", "defaultThreadPoolSize", 1));
+  }
+
+  public WorkQueue(IdGenerator idGenerator, int defaultThreadPoolSize) {
     this.idGenerator = idGenerator;
     this.queues = new CopyOnWriteArrayList<Executor>();
-    defaultQueueSize = cfg.getInt("execution", "defaultThreadPoolSize", 1);
+    this.defaultQueueSize = defaultThreadPoolSize;
   }
 
   /** Get the default work queue, for miscellaneous tasks. */