During an upgrade from Stein to Train, Kolla Ansible fails while running
TASK [cinder : Running Cinder online schema migration]

This is because the `--max_count 10` option is used, which returns 1
while migrations are processed. According to the upgrade documentation,
the command should be rerun while the exit status is 1:
https://docs.openstack.org/cinder/train/upgrade.html

This issue was introduced by a change to the image [1] which fixed a bug
in the way that the max count was interpreted, but exposed an issue in
using the max count.

This change fixes the issue by ceasing to pass MAX_NUMBER, which will
cause all migrations to occur in a single pass.

[1] https://review.opendev.org/#/c/712055

Change-Id: Ia786d037f5484f18294188639c956d4ed5ffbc2a
Closes-Bug: #1880753