ceph-volume: be idempotent when the batch strategy changes

ceph-volume: be idempotent when the batch strategy changes

If you deploy with 2 HDDs and 1 SDD then each subsequent deploy both
HDD drives will be filtered out, because they're already used by ceph.
ceph-volume will report this as a 'strategy change' because the device
list went from a mixed type of HDD and SDD to a single type of only SDD.

This situation results in a non-zero exit code from ceph-volume. We want
to handle this situation gracefully and report that nothing will be changed.
A similar json structure to what would have been given by ceph-volume is
returned in the 'stdout' key.

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1650306
Signed-off-by: Andrew Schoen <aschoen@redhat.com>