Fix overflowing journel partitions.

This fixes #896406. When useing ceph-disk to create a journel parititon
in the next available partition and thier is not enough space ceph-disk
did not provide a clear error message.

cherry picked from 05a4347f745f9d648acf67e25736d8d70cdc8f80 with
Conflicts on src/ceph-disk resolved.

Signed-off-by: Owen Synge <osynge@suse.com>