Add benchmarking code (#448)

* adding benchmarking code

* enable writing to file

* fix build

* time more stuff

* adding benchmarking to integration tests

* compare docker and kaniko times in integration tests

* Switch to setting benchmark file with an env var

* close file at the right time

* fix integration test with environment variables

* fix integration tests

* Adding benchmarking documentation to DEVELOPEMENT.md

* human readable benchmarking steps

cmd/executor/cmd/root.go

@@ -47,6 +47,7 @@ func init() {
 	addHiddenFlags(RootCmd)
 }
 
+// RootCmd is the kaniko command that is run
 var RootCmd = &cobra.Command{
 	Use: "executor",
 	PersistentPreRunE: func(cmd *cobra.Command, args []string) error {