create intermediate folders for cache_dir

[Simon-Reif]

got a file not found error before any jobs started
fixed it by replacing "os.mkdir(cache_dir)" with "os.makedirs(cache_dir)" in line 290 in cluster_utils/server/utils.py

[luator]

Thanks for the fix!

I have just one small change request: Please add an entry in the CHANGELOG.md file (in the "Unreleased" section), something like this:

### Fixed
- Fixed error if parent(s) of the cache directory do not exist.

[luator]

Thanks!