Fixed "recipe_content" path for 5-2-stable
update upgrade guide with backup, db specific commands, config changes, check, and restore
Merge pull request #4068 from bbodenmiller/update-upgrade-guide

update upgrade guide with backup, db specific commands, config changes, ...
Merge pull request #4045 from ymiyoshi/5-2-stable

Fixed "recipe_content" path of "check.rake" for 5-2-stable
improve regrex for match(sidekiq) robustness

e.g.: the sidekiq in my Debian box is v2.11.1
5-2-stable is working