- don't start/stop services - we assume appropriate services start/stop
  will be done bu invoker, and tell people to do so via dumping proper
  comments. (Rationale: services are start/stopped differently on
  different systems, e.g. in omnibus and in slapos)

- mv in repositories atomically with just 1 mv + fix case when there was
  no repositories/ previously at all.

- adjust `gitlab-rake gitlab:backup:restore` with force=yes, so it does
  not interactively ask about whether ok to restore ssh keys - just do it.

- add `-go` option to actually run gitlab restoration in addition to
  preparing backup files.

/cc @kazuhiko