When connection fails, try to recreate pgpass file.

When starting up stoq, if the connection to the database fails try to setup
the pgpass using the stored password the configuration wizard created.

Change-Id: I2908ee9f50aede3088e3e00a45961b11147095eb
(cherry picked from commit d0b71cb4867c226dc1e1697e6f8af08f44919230)