Fix HailContext construction from preconstructed spark contexts (#1507)
Fix HailContext construction from preconstructed spark contexts (#1507)


cseed/hail,hail-is/hail,cseed/hail,hail-is/hail,hail-is/hail,hail-is/hail,cseed/hail,hail-is/hail,hail-is/hail,cseed/hail,hail-is/hail,danking/hail,danking/hail,danking/hail,danking/hail,danking/hail,danking/hail,danking/hail,cseed/hail,cseed/hail,cseed/hail,danking/hail,hail-is/hail,cseed/hail