Transition user ldbd tasks to user segdb

User ldbd is a local account on a few segments* servers, created to run some tasks without root permissions. Now that there is a shared account, segdb, which is shared across all segments* servers, user ldbd's tasks should probably be migrated to user segdb (and some tasks run by root should be migrated, as well). Discussion of any reasons not to migrate such tasks should be done here.

User ldbd's tasks on segments.ligo.org:

• daily DB backup
• archive DB backups
• archive publisher logs
• archive Python server logs

User ldbd's tasks on segments-backup.ligo.org:

• restore the latest DB backup
• run the daily regression tests

User ldbd exists but has no tasks on segments-dev or segments-dev2.

User ldbd does not exist on segments-web.

Note that there is code in the SL7 installation script to create some of the infrastructure for user ldbd. Once it is no longer needed, that should be removed.