MAGETWO-59810: Reinstate DateTime instantiation fallback

Author: danmooney2

dev/tests/integration/testsuite/Magento/Framework/Stdlib/DateTime/Filter/DateTimeTest.php

@@ -71,6 +71,8 @@ public function localeDatetimeFilterProvider()
             ['fr_FR', '01/02/2010 1:00', '2010-02-01 01:00:00'],
             ['fr_FR', '01/02/2010 01:00', '2010-02-01 01:00:00'],
             ['de_DE', '01/02/2010 15:30', '2010-02-01 15:30:00'],
+            ['en_US', '2017-09-01T15:30:00.000Z', '2017-09-01 15:30:00'],
+            ['fr_FR', '2017-09-01T15:30:00.000Z', '2017-09-01 15:30:00'],
         ];
     }
 }

lib/internal/Magento/Framework/Stdlib/DateTime/Timezone.php

@@ -174,7 +174,7 @@ public function date($date = null, $locale = null, $useTimezone = true, $include
                     $timeType,
                     new \DateTimeZone($timezone)
                 );
-                $date = $formatter->parse($date);
+                $date = $formatter->parse($date) ?: (new \DateTime($date))->getTimestamp();
                 break;
         }