* parse arg commands at the top of dockerfiles
* fix pointer reference bug and remove debugging
* fixing tests
* account for meta args with no value
* don't take fs snapshot if / is the only changed path
* move metaArgs inside KanikoStage
* removing unused property
* check for any directory instead of just /
* remove unnecessary check
gometalinter is broken @ HEAD, and I looked into why that was. During
that process, I remembered that we took the linting scripts from
skaffold, and found that in skaffold gometalinter was replaced with
GolangCI-Lint:
https://github.com/GoogleContainerTools/skaffold/pull/619
The change made linting in skaffold faster, so I figured instead of
fixing gometalinter it made more sense to remove it and replace it with
GolangCI-Lint for kaniko as well.