[18.09 backport] builder / buildkit updates - #1438

[18.09 backport] builder / buildkit updates#1438

tiborvass merged 4 commits into

docker:18.09docker/cli:18.09from

thaJeztah:18.09_backport_hide-buildkit-flags-if-not-enabledthaJeztah/cli:18.09_backport_hide-buildkit-flags-if-not-enabledCopy head branch name to clipboard