gs_unittest: simplify stub tarball creation

This takes the runtime on my system from ~27s to ~8s, and makes the
output a lot less chatty.

BUG=None
TEST=`./run_tests` passes

Change-Id: I4f32f2d31d4afd3085d8abc40d823bee46033c7b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2386036
Tested-by: Mike Frysinger <vapier@chromium.org>
Auto-Submit: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Alex Klein <saklein@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
diff --git a/lib/gs_unittest.py b/lib/gs_unittest.py
index db323b0..05ec4b0 100644
--- a/lib/gs_unittest.py
+++ b/lib/gs_unittest.py
@@ -61,7 +61,9 @@
     tempfile = os.path.join(self.tempdir, 'tempfile')
     osutils.WriteFile(tempfile, 'some content')
     gsutil_path = os.path.join(self.tempdir, gs.GSContext.GSUTIL_TAR)
-    cros_build_lib.CreateTarball(gsutil_path, self.tempdir, inputs=[tempfile])
+    cros_build_lib.CreateTarball(
+        gsutil_path, self.tempdir, inputs=[os.path.basename(tempfile)],
+        compression=cros_build_lib.COMP_NONE)
     self.GSUTIL_URL = 'file://%s' % gsutil_path
 
   def PreStart(self):