Implement component upgrades

[xjia1]

Related to #11

• Keycloak -- export and import; see internal notes [1] and [2]; need to verify that this still works
• Gerrit -- https://www.gerritcodereview.com/3.8.html#important-notes; we will start with offline upgrades
• Redmine -- only needs to run rake db:migrate
• Buildbot -- do we really need to do anything special here?

And before any kinds of upgrade, the workdir must be archived for backup purposes. Downgrades are supposed to be done manually.

[xjia1]

This is not a release blocker