Also, I found this: https://wiki.zimbra.com/wiki/Sudoers
It suggest that I also change Defaults from env_reset to requiretty. Is this necessary?
Just ignore. I didn't bother that.
I have made 8.71 work on Ubuntu 14.04 for 2 weeks before I do-release-upgrade to Ubuntu 16.04.
I also experienced a couple of failures before success.