Add compatibility with erppeek 1.6b1 and Odoo 8.0

Adds compatibility with erppeek 1.6b1 and Odoo 8.0

This issue occured:

https://bugs.launchpad.net/oerpscenario/+bug/1360152

I'm not sure from where it comes but with erppeek 1.6b1 I was only able to use a string to have a working client.

This MP should wait on https://github.com/tinyerp/erppeek/pull/55