drop queries for full-refresh builds are not namespaced on pg/redshift

[drewbanin]

Describe the bug

When dbt replaces a view or table in an incremental build, it creates a backup_relation. This relation is intended to be dropped at the end of model build. Errantly, dbt created this backup_relation without a schema on postgres and redshift. This results in a (correct) rename query which looks like:

alter table schema.table rename to table__dbt_backup_20191118

but the corresponding drop at the end of the builds looks like:

drop table if exists table__dbt_backup_20191118

This second query is incorrect, as it this query is looking for a table called table__dbt_backup_20191118 in the public schema! As a result, full refresh builds on postgres + redshift may have been leaving backup tables in dbt schemas since at least 0.14.3, though possibly earlier.

Steps To Reproduce

Using 0.14.x, create an incremental model and run it with the --full-refresh flag a couple of times. You should see lingering backup tables in the dbt schema.

System information

Which database are you using dbt with?

• postgres
• redshift

[drewbanin]

this was fixed in #1931