This introduces a PRODUCT environment variable that is used to set a constant at dockerversion.ProductName. That is then used to set BuildKit's ExportedProduct variable in order to show useful error messages to users when a certain version of the product doesn't support a BuildKit feature. Signed-off-by: Tibor Vass <tibor@docker.com> Upstream-commit: 195919d9d645aa4ab5680a2331c57ff33eb9e5d9 Component: engine