* util/grub-fstest.c (execute_command): Make first argument

	* util/grub-fstest.c (execute_command): Make first argument
	a const char *.
	(read_file): Avoid shadowing.
	Reuse underlying error message if device open fails.
	(cmd_cmp): Respect format security.
	(root): Make const char *.
	(fstest): Remove args argument and use global copy.
	Respect format security.
	(argp_parser): Make static.
	(main): Make default_root const char *.