change tkn image set in makefile

[lilyLuLiu]

#279

[anjannath]

LGTM

so when we want to now push a released 8.0.0 image we can use, e.g make VERSION=8.0.0 tkn-push

[adrianriobo]

Also I notice the tkn-bundle/tkn-check passed but that should not be the case, as the spec do not contain a valid image on it, it just contains the <IMAGE> field as the tkn-template is not being used there.

We have to issues there:

• Ensure the template function is used somehow before they are deployed to the cluster on the check
• Look for a way to dry/run or some type of test which may does not require credentials / or something we can pass empty to test the task will be able to run.

[lilyLuLiu]

@adrianriobo , I keep the orignal tkn yaml files and use another folder to store the templates. So tkn-bundle/tkn-check can check the validation of the tkn file. Also add make tkn-update in makefile for updating the version for tkn.