The exampkle gertty yaml files indicate that there is a 'lock-file'
parameter per server that allows you to define the location of a
lockfile. Code to handle that exists in config.py but the option is not
defined in the schema, so errors like this cause the process to exit:
voluptuous.error.MultipleInvalid: extra keys not allowed @ data['servers'][0]['lock-file']
Change-Id: Ia03ed9d2de5d598eeafc6e8ffab30c99bd9fded6