conf: Validate '[api] vendordata_providers' options
conf: Validate '[api] vendordata_providers' options

Only two options are currently supported. Let's hardcode this behavior.

Change-Id: I7609f408294ca151db9b7ff43d8c7bf6a4638a94

rahulunair/nova,gooddata/openstack-nova,gooddata/openstack-nova,phenoxim/nova,rahulunair/nova,mahak/nova,gooddata/openstack-nova,mikalstill/nova,gooddata/openstack-nova,klmitch/nova,mikalstill/nova,phenoxim/nova,openstack/nova,mahak/nova,klmitch/nova,openstack/nova,klmitch/nova,rahulunair/nova,mikalstill/nova,mahak/nova,klmitch/nova,openstack/nova