[#62448006] make instance validate method private
[#62448006] make instance validate method private

... to clarify the usage of the interface - should call ConfigValidate.validate factory

gds-operations/vcloud-launcher,UKHomeOffice/vcloud-launcher,UKHomeOffice/vcloud-launcher,gds-operations/vcloud-launcher,gds-operations/vcloud-launcher,UKHomeOffice/vcloud-launcher