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>
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>