purge-cluster: do not include ceph-osd and ceph-common defaults for osds

purge-cluster: do not include ceph-osd and ceph-common defaults for osds

When purging OSDs we do not need to include these defaults as nothing in
the following tasks uses them. Also, it has the side effect of
overwriting any variables defined in group_vars files that are relative
to the inventory you are using with the default values. That behavior
was causing the CI tests to fail.

Signed-off-by: Andrew Schoen <aschoen@redhat.com>
(cherry picked from commit dd8389cdf7651f3bb9a02dc00c65bc48a5582bfd)