Some componentconfig options are aliased to native convertible types
(e.g. ProxyMode) but FindAndSet() was unable to detect that and so it
wasn't possible to set these values via `--extra-config`.
This change addresses that by using the reflected value's Kind instead
of a type assertion on its interface.
It's also worth noting that any value with the type Duration (e.g.
proxy.IPTablesSyncPeriod) is also unable to be set for the same reason,
but this commit does not address that.
See https://github.com/kubernetes/minikube/issues/1217
Matt Rickard
dlorenc
Dale Hamel
Eden Li
Jimmi Dyson
Dan Lorenc