mariadb-common: Drop package and adjust configuration

mariadb-common: Drop package and adjust configuration

The raison d'être of package mariadb-common was to provide common my.cnf
config file that was being used to include subdirectories and then to
push utf-8 as default everywhere. Let's make this file part of the
server package as there we actually set other options as well and drop
it from all clients. Instead let's set utf-8 as default in server,
client and client libraries. While at it also set socket to the more
common path and drop mysqld_safe script from the list of configuration
files and do other minor tweaks.

Signed-off-by: Michal Hrusecky <michal.hrusecky@turris.com>