selftests: ublk: reorganize tests into integrity and recover groups

selftests: ublk: reorganize tests into integrity and recover groups

Move integrity-focused tests into new 'integrity' group:
- test_null_04.sh -> test_integrity_01.sh
- test_loop_08.sh -> test_integrity_02.sh

Move recovery-focused tests into new 'recover' group:
- test_generic_04.sh -> test_recover_01.sh
- test_generic_05.sh -> test_recover_02.sh
- test_generic_11.sh -> test_recover_03.sh
- test_generic_14.sh -> test_recover_04.sh

Update Makefile to reflect the reorganization.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>