Added netinfoTests:testGetEmpty

The new test should prevent the regression introduced in:
http://gerrit.ovirt.org/#/c/21652/

And fixed in:
http://gerrit.ovirt.org/#/c/21850/

Change-Id: Ibfb1d18eeb697de6bf8d35ab9748a61324fde9ac
Signed-off-by: Assaf Muller <amuller@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/21881
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>