Adding TTL to caching (#488)

* Adding TTL to caching

* uncomment added lines

* cache TTL works for layers now

* remove debugging

* parse booleans correctly

* parse booleans correctly everywhere

* fix boolean parsing condition

* refactor benchmarking calls

* defer file properly

cmd/executor/cmd/root.go

@@ -21,6 +21,7 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"time"
 
 	"github.com/GoogleContainerTools/kaniko/pkg/buildcontext"
 	"github.com/GoogleContainerTools/kaniko/pkg/config"
@@ -109,6 +110,7 @@ func addKanikoOptionsFlags(cmd *cobra.Command) {
 	RootCmd.PersistentFlags().StringVarP(&opts.CacheDir, "cache-dir", "", "/cache", "Specify a local directory to use as a cache.")
 	RootCmd.PersistentFlags().BoolVarP(&opts.Cache, "cache", "", false, "Use cache when building image")
 	RootCmd.PersistentFlags().BoolVarP(&opts.Cleanup, "cleanup", "", false, "Clean the filesystem at the end")
+	RootCmd.PersistentFlags().DurationVarP(&opts.CacheTTL, "cache-ttl", "", time.Hour*336, "Cache timeout in hours. Defaults to two weeks.")
 }
 
 // addHiddenFlags marks certain flags as hidden from the executor help text