Update NEWS file for 2.9.7 release
Update NEWS file for 2.9.7 release

... with security release info and minor changes.

Signed-off-by: Hrvoje Ribicic <be5828fca31f89218048bec4189e30a581aa65da@google.com>
Reviewed-by: Helga Velroyen <2d0126b1ec6f9ec5cbec4a7012aa14faeaef10f5@google.com>
Reviewed-by: Oleg Ponomarev <c100474c6090841e9d55cde74d38d81efd269b8d@google.com>

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