From depth of the galaxy, your call I heard my young padawan 
If I am not wrong, MariaDB root user can only connect through unix socket and not from a TCP one like 127.0.0.1 on Ubuntu servers.
On your mysql status command:
mysql > status
(...)
Connection: Localhost via UNIX socket
(...)
If you try to connect as mysql root user with -h 127.0.0.1 argument, it will fail on Ubuntu.
By the way, using mysql root user can seems easier, but this is definitively the path to the dark side of the Force. You should use the dedicated mariadb user created at this step of the documentation:
This is the way 
And the dedicated user will be able to connect to 127.0.0.1.
May the Force be with you, always.