[FEATURE REQUEST] Support ERB in database config yml file for tests

[arielj]

It is common in Rails to include ERB code inside the config/database.yml file.

Doing the same when running tests for this gem and the different parts like database_cleaner-active_record does not support using ERB and it's considered part of the values, like... doing password: <%= ENV["MYSQL_PASSWORD"] || "" %> sets the literal "<%= ENV["MYSQL_PASSWORD"] || "" %>" string as the value instead of getting the value from the ENV or having a fallback.