Removal of the config.Config from blob package

As we are ready to get rid of the global config.Config variable this change does exact it for the files in the blob package. It also includes some small refactorings like adding a setup function, renames and marking functions as test-helpers.

The tests that are dependent on the gitaly-ruby process now aggregated into a single test that starts gitaly-ruby process before run with the default configuration. Global rubyServer variable removed because gitaly-ruby service is passed as a parameter into the dependent tests together with the base configuration.

The testhelper.DefaultLocator() was removed because it has no usages anymore.

Part of: #2699 (closed)