QA: Allow logging at different log levels
Problem to solve
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/22084 implements basic debug logging. But when enabled it's very verbose and there's only one level - all or nothing.
@logger.level = ::Logger.const_get((ENV['QA_LOG_LEVEL'] || 'DEBUG').upcase)
...If nothing set, no log. If it's set, it should be either DEBUG, INFO, and so on.
For consistency we may want to use
Runtime::Env instead of accessing