message: test: fix a bug in tests for compressed cache file
  The json configuration for compressed cache file is wrong, so fix it
  enable test cases for compressed cache files.
diff: @@ -32,8 +32,8 @@ pub fn new(
  r###"
  ,"cache": {{
  "type": "blobcache",
  - "config": {{
  "compressed": {},
  + "config": {{
  "work_dir": {:?}
  }}
  }}
  @@ -49,8 +49,7 @@ pub fn new(
  "backend": {{
  "type": "localfs",
  "config": {{
  - "dir": {:?},
  - "readahead": true
  + "dir": {:?}
  }}
  }}
  {}
  