Prepare NEWS file for 2.11.1
Prepare NEWS file for 2.11.1

Prepare the NEWS file for the release of 2.11.1, that is
add release date and changes since the last release.

Signed-off-by: Helga Velroyen <2d0126b1ec6f9ec5cbec4a7012aa14faeaef10f5@google.com>
Reviewed-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>

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