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: Ib22685902103d2a2b9f032a25de19e92b40e8154
Closes-Bug: #1517839
5bcd8c6f1a