engine: resources: Remove named return params

Named return params aren't a favourite feature of mine, and they're
rarely used in the resource writing. They keep popping up because I once
used them and we've been copying and pasting code ever since. Get rid of
them all to help prevent the unnecessary spread.

engine/resources/docker_container.go

@@ -201,7 +201,7 @@ func (obj *DockerContainerRes) Watch() error {
 }
 
 // CheckApply method for Docker resource.
-func (obj *DockerContainerRes) CheckApply(apply bool) (checkOK bool, err error) {
+func (obj *DockerContainerRes) CheckApply(apply bool) (bool, error) {
 	var id string
 	var destroy bool