Ignore corrupt cache control data; re-download file

Fixes CHEF-4365: http://tickets.opscode.com/browse/CHEF-4365

A corrupt cache control file will cause a persistent failure of the
related remote_file resource. Since this data is just a cache of HTTP
headers, Chef can ignore corrupted cache control data, re-download the
source file, and then re-populate the cache with not-corrupt data.
Merge branch 'CHEF-4365'