ceph-disk: fix verify_no_in_use check

We only need to verify that partitions aren't in use when we want to
consume the whole device (osd data), not when we want to create an
additional partition for ourselves (osd journal).

Backport: firefly
Signed-off-by: Sage Weil <sage@redhat.com>
(cherry picked from commit d6e6ba198efc4b3afff0c70af53497a70c6b3f19)
Revert "Fix for bug #6700"

This reverts commit 673394702b725ff3f26d13b54d909208daa56d89.

This appears to break things when the journal and data disk are *not* the same.
And I can't seem to reproduce the original failure...

Signed-off-by: Sage Weil <sage@redhat.com>
(cherry picked from commit 2edf01ffa4a7425af2691b4e94bc5fd0bfab1e5b)