tests: Add cryptomount functional test

tests: Add cryptomount functional test

The grub_cmd_cryptomount make check test performs some functional testing
of cryptomount and by extension the underlying cryptodisk infrastructure.

A utility test script named grub-shell-luks-tester is created to handle the
complexities of the testing, making it simpler to add new test cases in
grub_cmd_cryptomount.

Signed-off-by: Glenn Washburn <development@efficientek.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>