generic/765: adjust various things

generic/765: adjust various things

Fix some bugs when detecting the atomic write geometry, record what
atomic write geometry we're testing each time through the loop, and
create a group for atomic writes tests.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>
Reviewed-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>