pgbench: Add TAP tests to check consistency of data generated
The tables created by pgbench rely on a few assumptions for TPC-B, where
the "filler" attribute is used to comply with this benchmark's rules as
well as pgbencn historical behavior. The data generated for each table
uses this filler in
pgbench: Use COPY for client-side data generation
This commit switches the client-side data generation from INSERT queries
to COPY for the two tables pgbench_branches and pgbench_tellers.
pgbench_accounts was already using COPY.
COPY is a better interface for bulk loading or high latency connecti
