Make bucket unit tests more useful (#1467)
Make bucket unit tests more useful (#1467)

Add a real test for `fetch`.
Don't use full URLs in paths within the bucket.
quiltdata/quilt-compiler,quiltdata/quilt,quiltdata/quilt,quiltdata/quilt,quiltdata/quilt-compiler,quiltdata/quilt-compiler,quiltdata/quilt,quiltdata/quilt-compiler,quiltdata/quilt