These tests have been failing intermittently since
3574a1be was merged.

They replace the connection handler during setup, but before that can
happen the existing handler's pool configuration has already been saved
by `setup_shared_connection_pool`. Later when the test calls
`teardown_shared_connection_pool`, it tries to restore connection pools
that do not exist in the new handler and blows up.

We can avoid this problem by calling `teardown_shared_connection_pool`
to clear the saved pools before replacing the connection handler.