Move UnixFileSystem to lib.unix, WindowsFileSystem to lib.windows

--
PiperOrigin-RevId: 148749485
MOS_MIGRATED_REVID=148749485
diff --git a/src/test/java/com/google/devtools/build/lib/testutil/TestConstants.java b/src/test/java/com/google/devtools/build/lib/testutil/TestConstants.java
index 3294d09..52cf1ba 100644
--- a/src/test/java/com/google/devtools/build/lib/testutil/TestConstants.java
+++ b/src/test/java/com/google/devtools/build/lib/testutil/TestConstants.java
@@ -63,7 +63,7 @@
   public static final String TEST_RULE_MODULE =
         "com.google.devtools.build.lib.bazel.rules.BazelRulesModule";
   public static final String TEST_REAL_UNIX_FILE_SYSTEM =
-      "com.google.devtools.build.lib.vfs.UnixFileSystem";
+      "com.google.devtools.build.lib.unix.UnixFileSystem";
 
   public static final ImmutableList<String> IGNORED_MESSAGE_PREFIXES = ImmutableList.<String>of();