[FIX] models: simplify partial setup of fields, let it crash silently

The setup of relational fields may be problematic, as they may refer to unknown
models via custom relational fields.  In a partial setup, do not try to skip
the field setup, but let it go and silently catch any exception if it crashes.
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-win32