Update NEWS for 2.12.2
Update NEWS for 2.12.2

.. with the latest bugfixes and known issues.

Signed-off-by: Petr Pudlak <9d19625f8ee825a2c398462ed335cbcf98f79c32@google.com>
Reviewed-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>

mbakke/ganeti,ganeti/ganeti,grnet/snf-ganeti,onponomarev/ganeti,andir/ganeti,dimara/ganeti,bitemyapp/ganeti,bitemyapp/ganeti,mbakke/ganeti,leshchevds/ganeti,yiannist/ganeti,mbakke/ganeti,leshchevds/ganeti,yiannist/ganeti,dimara/ganeti,grnet/snf-ganeti,andir/ganeti,yiannist/ganeti,ganeti/ganeti,leshchevds/ganeti,andir/ganeti,ganeti/ganeti,onponomarev/ganeti