Fix unrecognized 'Z' UTC designator

closes #8771 
ahh, so the fallback was producing an incorrect result (e.g. dateutil). not surprised. Ok so that we KNOW that these 2 cases are not legit. Is it easy to catch these 2 cases? (eg. either you have Z then end-of-string, or Z legit value?) (maybe just easy to simply test if 0/00 are present after Z and raise).