Measurement of the $ZZ$ production cross section in proton- proton collisions at $\sqrt s =$ 8 TeV using the $ZZ\to\ell^{- }\ell^{+}\ell^{\prime -}\ell^{\prime +}$ and $ZZ\to\ell^{- }\ell^{+}\nu\bar{\nu}$ channels with the ATLAS detector