Fix when we VACUUM ANALYZE. (#228)

Careful reading of the Explicit Locking chapter of Postgres documentation
shows that VACUUM and ANALYZE take a SHARE UPDATE EXCLUSIVE lock against the
target table, and CREATE INDEX take a SHARE lock, which conflicts with the
former one.

  https://www.postgresql.org/docs/current/explicit-locking.html

So we can't actually VACUUM ANALYZE a table while building the indexes and
then constraints on top of that. The queueing of the VACUUM operations is
now done after the indexes and constraints are built.