test: make enforce_type=True in CONF.set_override
test: make enforce_type=True in CONF.set_override

each config option has limitation for type and value. In production
code, oslo.conf can ensure user's input is valid, but in unit test,
test methods can pass if we use method CONF.set_override without
parameter enforce_type=True even we pass wrong type or wrong value
to config option. This commit makes sure calling method
CONF.set_override with enforce_type=True

Change-Id: Ia1511c1e1db53c83c8745134804aa09c7d2a3408
Related-Bug: #1517839

openstack/designate,grahamhayes/designate,grahamhayes/designate,openstack/designate,openstack/designate,grahamhayes/designate