Update NEWS file for 2.17
Update NEWS file for 2.17

Add infos about MaintD, N+M redundancy and --avoid-disk-moves option
for hbal.

Signed-off-by: Lisa Velden <f95ae155456787aef400a49db463a62bbef84ead@google.com>
Reviewed-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>

andir/ganeti,onponomarev/ganeti,mbakke/ganeti,leshchevds/ganeti,leshchevds/ganeti,leshchevds/ganeti,onponomarev/ganeti,andir/ganeti,ganeti/ganeti,ganeti/ganeti,andir/ganeti,ganeti/ganeti,mbakke/ganeti,mbakke/ganeti