Foreman Maintain

Full upgrade scenario

This commit intoroduces more structured upgrade scenario consisting of
this scenarios:

• pre_upgrade_check - non-modifying checks: is the system ready?
• pre_migrations - modifying procedures before source update
• migrations - source update and main migrations...

Fixes #44 - Change tag 'basic' to 'default'

Done changes for rubocop v0.48.1

Compatiblity with rubocop v0.48.0

1. Disabled: Use %i or %I for an array of symbols
2. Fixed: Use 2 spaces for indentation in a heredoc by using some library(e.g. ActiveSupport's String#strip_heredoc). Created foreman_maintain/core_ext.rb extend String class....

Add tests for empty args in cli

Allow running checks by label

Add scaffold for definitions tests