Hi,
firstly welcome to the forum, have a read of this post...
Plesk 12 with Mariadb on Ubuntu 14.04
# dpkg -i --force-overwrite /var/cache/apt/archives/libmysqlclient18_10.1.18+maria-1~trusty_amd64.deb
When that returns and error, run...
# dpkg --configure -a
That too will find an error...