Fix executor Dockerfile, which wasn't building (#1741)
Fix executor Dockerfile, which wasn't building (#1741)

The Makefile from the `docker-credential-gcr` repo was removed, so all builds were failing. This PR removes the `make` command and pins `docker-credential-gcr` to a specific commit so that this doesn't happen again.
GoogleContainerTools/kaniko,GoogleContainerTools/kaniko,GoogleContainerTools/kaniko