Update NEWS for 2.7.0~beta3
Update NEWS for 2.7.0~beta3

- Most entries for beta1 are moved to the top level
- The beta1 to beta2 delta is left

Signed-off-by: Guido Trotter <f62ca4d5358bdaeef0e50e57f9f7e231de63727e@google.com>
Reviewed-by: Michele Tartara <05f7077a2c6cbbdc4af4ba42e3ef89a0df846179@google.com>

leshchevds/ganeti,ganeti-github-testing/ganeti-test-1,mbakke/ganeti,andir/ganeti,yiannist/ganeti,apyrgio/ganeti,andir/ganeti,andir/ganeti,ganeti/ganeti,bitemyapp/ganeti,leshchevds/ganeti,yiannist/ganeti,apyrgio/snf-ganeti,leshchevds/ganeti,onponomarev/ganeti,apyrgio/ganeti,ganeti/ganeti,ganeti-github-testing/ganeti-test-1,mbakke/ganeti,grnet/snf-ganeti,mbakke/ganeti,yiannist/ganeti,onponomarev/ganeti,grnet/snf-ganeti,dimara/ganeti,bitemyapp/ganeti,ganeti/ganeti,dimara/ganeti,apyrgio/snf-ganeti