Replace gometalinter with GolangCI-Lint

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.

pkg/config/options.go

@@ -19,16 +19,16 @@ package config
 // KanikoOptions are options that are set by command line arguments
 type KanikoOptions struct {
 	DockerfilePath string
-	Destinations   multiArg
 	SrcContext     string
 	SnapshotMode   string
 	Bucket         string
-	InsecurePush   bool
-	SkipTlsVerify  bool
-	BuildArgs      multiArg
 	TarPath        string
+	Target         string
+	Destinations   multiArg
+	BuildArgs      multiArg
+	InsecurePush   bool
+	SkipTLSVerify  bool
 	SingleSnapshot bool
 	Reproducible   bool
-	Target         string
 	NoPush         bool
 }

pkg/config/stage.go

@@ -21,8 +21,8 @@ import "github.com/moby/buildkit/frontend/dockerfile/instructions"
 // KanikoStage wraps a stage of the Dockerfile and provides extra information
 type KanikoStage struct {
 	instructions.Stage
+	BaseImageIndex         int
 	FinalStage             bool
 	BaseImageStoredLocally bool
-	BaseImageIndex         int
 	SaveStage              bool
 }