If you have a "service/configurations.yml" file, but every single line is
commented out, then an error occurs when running tests:
```
git:active-storage-import~/code/rails/activestorage$ rake
~/code/rails/activestorage/test/test_helper.rb:17:in `<top (required)>': undefined method `deep_symbolize_keys' for false:FalseClass (NoMethodError)
from ~/code/rails/activestorage/test/controllers/direct_uploads_controller_test.rb:1:in `require'
```
The reason is that `YAML.load(..an empty file content..)` simply returns `false`, and not `{}`.
This PR fixes this behavior so tests can also run when no remote service
is available.
