workers: Make sure to wait for worker processes to exit so that they don't become zombies.

--
MOS_MIGRATED_REVID=103541217
diff --git a/src/test/java/com/google/devtools/build/lib/shell/InterruptibleTest.java b/src/test/java/com/google/devtools/build/lib/shell/InterruptibleTest.java
index 8192bd9..4e864a9 100644
--- a/src/test/java/com/google/devtools/build/lib/shell/InterruptibleTest.java
+++ b/src/test/java/com/google/devtools/build/lib/shell/InterruptibleTest.java
@@ -27,7 +27,7 @@
 /**
  * Tests of the interaction of Thread.interrupt and Command.execute.
  *
- * Read http://www-128.ibm.com/developerworks/java/library/j-jtp05236.html
+ * Read http://www.ibm.com/developerworks/java/library/j-jtp05236/
  * for background material.
  *
  * NOTE: This test is dependent on thread timings.  Under extreme machine load