xfs/259: test more block sizes and handle minimum block size correctly

xfs/259: test more block sizes and handle minimum block size correctly

Currently xfs/259 tests against TEST_DIR for CRC support status to
decide whether 512 block size should be tested, which is wrong for this
test, because configuration of TEST_DIR is not controlled by test
harness and can be different to the configuration being used in the
test.

Fix it by reversing the block size order that's tested and capture the
output of the actual mkfs command that is being tested, and determine if
512 byte block sizes should be tested based on that output.

While we're at it, I think the test matrix can be enlarged as well, 4k,
2k, 1k and 512 block size can be tested in each fs size boundary, not
only the minimum block size.

Suggested-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>