Add strip size support to rbd driver

Rbd support strip size for volume, in general, we would like to think the
default value 4M is a proper for most of users.

In the ceph side, the proper value of rbd strip size can improve performance for
the special OSD backend.

Implements blueprint add-rbd-strip-size

Change-Id: I44d89681a78bd70d8c185e3da7d58f59e6076899
Signed-off-by: Haomai Wang <haomai@unitedstack.com>
Merge "Add strip size support to rbd driver"