Use database_cleaner on specs

[rafaels88]

Today our specs are implementing an own database cleaner helper to clean the tables on each spec. But it is badly implemented, since it is necessary to call the helper on every spec file, and it is looping on every repository to call for each repo object and clean its database. Yes, it is dummy.

This task is about to replace this implementation to use the database_cleaner gem https://github.com/DatabaseCleaner/database_cleaner