disk storage: symlink logic fails if using relative directories

[srenatus]

With an OPA config like

services:
  bundles:
    url: http://127.0.0.1:8000
bundles:
  perms:
    service: bundles
    resource: simple.tar.gz
storage:
  disk:
    directory: _tmp_simple
    auto_create: true

the server would create a symlink of

active -> _tmp_simple/backupXXXX

after successful bundle activation.

On restart, it would try to resolve _tmp_simple/active, and fail to find _tmp_simple/_tmp_simple/active:

error: initialize disk store: storage_internal_error: lstat _tmp_simple/_tmp_simple: no such file or directory

A workaround is to configure disk storage with absolute paths instead; the symlink will then be properly created.

Once the symlink is wrong, however, it needs to manually be fixed. In the _tmp_simple example above, that would be

rm _tmp_simple/active
ln -s backupXXXXX _tmp_simple/active