TESTS: Add tests that get_lba_status for a single range works

Add a test for unmapping a single range of blocks and that
get_lba_status returns correct data.

Test unmapping a single block at offsets 0-255

Test unmapping 1-255 blocks at offset 0 and verify that
get_lba_status at LBA 0 returns a descriptor of 1-255 blocks.
get_lba_status at the last block of the unmapped range returns
a descriptor for a single block.

Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>