LP#1271661: Use unlogged tables to avoid lock churn

LP#1271661: Use unlogged tables to avoid lock churn

Attempting to load a large number of bib records into a Vandelay
import queue can stall and fail, with no records getting staged
into the import queue.  It is suspected that this is because of the
locks required to maintain temp tables, which we create and destroy
for each record we look at.  Instead, let's just use unlogged tables
and empty them explicitly after each record.  Autovacuum should
protect us from bloat growth.

Signed-off-by: Mike Rylander <mrylander@gmail.com>