Well the issue is user zentyal has no perms, we know what users have access, root, the issue is that the root pass listed is not correct.
OP: Create a new user for mysql, and as su grant all perms (in mysql), so it acts like root. Dont change anything else as zentyal relies on some stuff for its databases. Root pass does not work, even when you change the pass, the hash is still the same, so somewhere along the line zentyal forces the orig pass, though that pass does not seem to work. Very strange, but all part of the fun.
Edit 2: Start mysql in safe mode to do all this, that works, though ymmv since it is super wonky on this build. BUT once set up it works very well, with only a few issues I can see in the logs. phpmyadmin works, the whole 9 yards, you just have to set up a user that has root privileges. Id also suggest setting an admin group and restricting users from using su or acting as root just for hardening purposes, so the user you create doesnt become a liability.