Fix overflowing journel partitions.

When using ceph-disk to create a journal partition in the next available
partition and thier is not enough space ceph-disk did not provide a clear
error message.

Signed-off-by: Owen Synge <osynge@suse.com>
I am afraid I don’t know where this was reported as I am working on SUSE linux.

# work around buggy libreadline(?) library in rhel/centos.

Comes from similar code, on line 955 of the same file in the function get_free_partition_index(dev):

Sadly this code also has no bug reference also.