Die gracefully or print when database is not available

[jerome]

When the cupspykota backend runs, we know that we need read+write access to the database. Introduce a printingwithnodb directive which allows either print or fail (and possibly ignore which is fail with an exit(0)), as values in pykota.conf. This directive will let PyKota know if it has to fail (as it does actually), or print anyway if the database isn't available.

[jerome]

Changed this to cover the case where no database is available at all : for example the database was manually shut down by the administrator but he forgot to disable printing as well. The ignore value may not be a good idea, and even with the print value at the very least a warning should be sent to the administrator.