Potential SA pool overflow

[nrueff]

When attempting to create a bundle on several (10 in my case) packages, the following error sometimes occurs:

ERROR SendPackageCommand: [Failure instance: Traceback: sqlalchemy.exceptions.TimeoutError: QueuePool LIMIT of size 5 overflow 10 reached, connection timed out, timeout 30

As a bundle is made of several commands, all of them spawned using deferreds, in some situation each command creation may use a SQ connection, leading to a short-term db pool exhausting.

Using a sequential algorithm for commands creation may resolve this problem.