Make CacheManagerTest write to cache directly.

Rather than using the Apache HTTP stack to load data into the cache,
we now call createCacheFile and saveCacheFile directly. This means
the same test works with both the Apache and Chromium HTTP stacks.

Bug: 3270236

Change-Id: I3c7ce91745fbdf6455f2e73d99d70848901eab92
1 file changed