Update testListFilesInRootDirectory to match reality

In the built-in UNIX filesystem, the newDirectoryStream method
will return absolute paths if given absolute paths as input,
and relative paths if given relative paths as input.

We're now seeing this too for the NIO Cloud Storage provider
(this is a good thing), so I updated this test to reflect
this new reality.

google-cloud-clients/google-cloud-contrib/google-cloud-nio/src/test/java/com/google/cloud/storage/contrib/nio/it/ITGcsNio.java

@@ -54,6 +54,7 @@
 import java.nio.file.Files;
 import java.nio.file.NoSuchFileException;
 import java.nio.file.Path;
+import java.nio.file.Paths;
 import java.nio.file.SimpleFileVisitor;
 import java.nio.file.StandardCopyOption;
 import java.nio.file.StandardOpenOption;
@@ -615,11 +616,17 @@ public void testListFilesInRootDirectory() throws IOException {
     // test absolute path, relative path.
     for (String check : new String[]{".", "/", ""}) {
       Path rootPath = fs.getPath(check);
-      List<String> objectNames = new ArrayList<>();
+      List<Path> pathsFound = new ArrayList<>();
       for (Path path : Files.newDirectoryStream(rootPath)) {
-        objectNames.add(path.toString());
+        // The returned paths will match the absolute-ness of the root path
+        // (this matches the behavior of the built-in UNIX file system).
+        assertWithMessage("Absolute/relative for " + check + ": ")
+            .that(path.isAbsolute()).isEqualTo(rootPath.isAbsolute());
+        // To simplify the check that we found our files, we normalize here.
+        pathsFound.add(path.toAbsolutePath());
       }
-      assertWithMessage("Listing " + check + ": ").that(objectNames).containsExactly(BIG_FILE, SML_FILE);
+      assertWithMessage("Listing " + check + ": ").that(pathsFound).containsExactly(
+          fs.getPath(BIG_FILE).toAbsolutePath(), fs.getPath(SML_FILE).toAbsolutePath());
     }
   }