Currently, when 'nova-manage db archive_deleted_rows' is run with
the --until-complete option, the process will archive rows in batches
in a tight loop, which can cause problems in busy environments where
the aggressive archiving interferes with other requests trying to write
to the database.
This adds an option for users to specify an amount of time in seconds
to sleep between batches of rows while archiving with --until-complete,
allowing the process to be throttled.
Closes-Bug: #1912579
Change-Id: I638b2fa78b81919373e607458e6f68a7983a79aa
fc77ce191f