Hide --clear-cache flag for build and run

[buildpacks/roadmap#30]

Signed-off-by: Andrew Meyer <ameyer@pivotal.io>

cmd/pack/main.go

@@ -119,6 +119,7 @@ func buildCommandFlags(cmd *cobra.Command, buildFlags *pack.BuildFlags) {
 	cmd.Flags().StringVar(&buildFlags.EnvFile, "env-file", "", "Build-time environment variables file\nOne variable per line, of the form 'VAR=VALUE' or 'VAR'\nWhen using latter value-less form, value will be taken from current\n  environment at the time this command is executed")
 	cmd.Flags().BoolVar(&buildFlags.NoPull, "no-pull", false, "Skip pulling images before use")
 	cmd.Flags().BoolVar(&buildFlags.ClearCache, "clear-cache", false, "Clear image's associated cache before building")
+	_ = cmd.Flags().MarkHidden("clear-cache")
 	cmd.Flags().StringSliceVar(&buildFlags.Buildpacks, "buildpack", nil, "Buildpack ID, path to directory, or path/URL to .tgz file"+multiValueHelp("buildpack"))
 }