Fix CMS cache path permissions

[matze]

The CMS we are using for static content attempts to create a directory for intermediate files, e.g. /var/cache/$repository. Since the associated scripts are not executed as user root, which is the only one allowed to change the fist-level content of /var/cache, this operation fails due to insufficient permissions.

Workaround

Create the respective sub-directory in manual fashion upfront.

Todo

• Extend class web::server to include the creation of /var/cache/$repository
• Ensure the cache directory is owned or just writable by user www
• Suggest the use of a distinct sub-directory, e.g. /var/cache/cms, or providing a configuration option, at least

[matze]

​https://hg.adblockplus.org/infrastructure/rev/bc42b98931a9

[matze]

Follow-up suggested in #3198.