Add Logger to GitLab QA

GitLab QA currently uses puts to output relevant information. This MR adds Logger to the framework enabling the possibility to use different log levels, increase readability by formatting the log message, and standardization on messages that can potentially help to debug issues.

As a bonus, the gem rainbow is added to colorize logs to improve scanning streams of information. This is left switched off by default for now.

There is a counterpart MR for GitLab, helping to equalize logging approaches (including documentation).