tests: Add test for iso9660 delayed CE hop

tests: Add test for iso9660 delayed CE hop

The ISO filesystem image iso9660_early_ce.iso exposes the unusual
situation that the Rock Ridge name entry of its only file is located
after a CE entry which points to the next continuation area.

The correct behavior is to read the Rock Ridge name and to only then
load the next continuation area. If GRUB performs this correctly, then
the name "RockRidgeName:x" will be read and reported by grub-fstest.
If GRUB wrongly performs the CE hop immediately when encountering the CE
entry, then the dull ISO 9660 name "rockridg" will not be overridden and
be put out by grub-fstest.

Signed-off-by: Thomas Schmitt <scdbackup@gmx.net>
Tested-by: Lidong Chen <lidong.chen@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>