The new config option 'disabled_drivers' is designed to address a
typical user case: As cloud provider, I'd like to only provide
some particular drivers, e.g. fedora atomic/k8s and don't expose
any other driver support. With this patch, when user create a new
template which is in 'disabled_drivers'. A BadRequest error will
be returned.
Closes-Bug: #1746961
Change-Id: Ib4c53ffed78a1847b2da9672e6348c88757ad66e