Migrated tests in devtools/build/lib/actions to JUnit 4.

In this case, it's more about fixing the setUp() methods (making them final and renaming them, wherever possible.)

--
MOS_MIGRATED_REVID=109079801
diff --git a/src/test/java/com/google/devtools/build/lib/actions/ArtifactTest.java b/src/test/java/com/google/devtools/build/lib/actions/ArtifactTest.java
index ec0b924..81fabbb 100644
--- a/src/test/java/com/google/devtools/build/lib/actions/ArtifactTest.java
+++ b/src/test/java/com/google/devtools/build/lib/actions/ArtifactTest.java
@@ -50,7 +50,7 @@
   private Root rootDir;
 
   @Before
-  public void setUp() throws Exception {
+  public final void setRootDir() throws Exception  {
     scratch = new Scratch();
     execDir = scratch.dir("/exec");
     rootDir = Root.asDerivedRoot(scratch.dir("/exec/root"));