Ignore interval_length attribute

Commit naparuba/shinken@f1452b2229 introduced a bug in this module. It adds interval_length attribute to program_status and update_program_status broks.

The NDO database schema doesn't have an interval_length column in the nagios_programstatus table. Because of that, inserts and updates on this table fail.

Here is a patch that adds this attribute to the ignore list.

I suspect that mod-ndodb-oracle has the same problem.

Second commit is PEP 8 reformatting.