Support binds in container exec command

This addresses issue #88.

internal/app/wwctl/container/exec/child/root.go

@@ -10,10 +10,11 @@ var (
 		Args:               cobra.MinimumNArgs(1),
 		FParseErrWhitelist: cobra.FParseErrWhitelist{UnknownFlags: true},
 	}
+	binds []string
 )
 
 func init() {
-
+	baseCmd.PersistentFlags().StringArrayVarP(&binds, "bind", "b", []string{}, "bind points")
 }
 
 // GetRootCommand returns the root cobra.Command for the application.