Use "no-cache" in the buildkit based builds
Use "no-cache" in the buildkit based builds

We now build three images using buildkit. The first one is
successful, but the 2nd one fails with 401.
I'm not sure why exactly, but the only way to make that work
is to pass the `--no-cache` flag, which appartently forces
buildkit to obtain a fresh auth token.

Signed-off-by: Andrea Frittoli <4cec69a2e3f23b658ef5550bf7c5b5012f9473f7@uk.ibm.com>

tektoncd/pipeline,tektoncd/pipeline