make sure you do not allow single IPs for new

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>
some tests for the new IP verification

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>
update the changelog

Signed-off-by: Alfredo Deza <alfredo.deza@inktank.com>
Merge pull request #58 from alfredodeza/5763-2

really complain about `ceph-deploy new [IP]`