Ctrl-c will leave storage_server.json lying around

If user stops `everest results` or `ert gui` with `ctrl-c`, any started dark storage will also be killed. But it will be killed in a not so nice manner leaving `storage_server.json` behind. When user subsequently starts again in the same directory, the now non-functional storage_server.json is picked up and attempted used.

After a timeout, ert/everest gives up, and gives a TimeoutError (and also deletes the non-functional json-file)

Reproduce the issue through the `everest results` and `ert gui` entry points by stopping a run with Ctrl-C, then inspect how the dark storage process and `storage_server.json` are handled. The fix is complete when interrupting either command does not leave a non-functional JSON file that breaks a subsequent start, while the existing timeout cleanup still works.

Written by the indexing model from the issue text.