tests: fix post and pool version tests helpers.

* Fix the pool version SQS service to always be mocked before every
  test. Before we had to manually set it up before every test dealing
  with pool versions.

* Fix it so that we reconnect to the post/pool version databases before
  every test. Before using $ARCHIVE_DATABASE_URL to set the database url
  failed because environment variables weren't loaded by dotenv yet when
  connections were first established.

test/unit/pool_test.rb

@@ -8,14 +8,9 @@ class PoolTest < ActiveSupport::TestCase
     end
 
     CurrentUser.ip_addr = "127.0.0.1"
-
-    mock_pool_archive_service!
-    PoolVersion.sqs_service.stubs(:merge?).returns(false)
-    start_pool_archive_transaction
   end
 
   teardown do
-    rollback_pool_archive_transaction
     CurrentUser.user = nil
     CurrentUser.ip_addr = nil
   end