Set trusted flag for configure-mirrors test
Set trusted flag for configure-mirrors test

As our mirrors aren't signed, we need to set this flag in order for
tests to pass when running on Ubuntu Bionic.

Change-Id: I2cbbda65e69f1f055d62e06286add215f9182102

openstack-infra/openstack-zuul-jobs,openstack-infra/openstack-zuul-jobs