We used to set query_cache_type to 0 in the default settings but we were
also setting query_cache_size to a non-zero/non-default value, which was
in turn re-enabling the query cache. Update the configuration to reflect
the actual cache state and make sure query_cache_size is set to zero for
the "query_cache_type = 0" case.

Now that the setting controls the real state of the query cache, disable
it for bbs.archlinux.org; its hit rate is small compared to insert rate.

The prometheus-mysqld-exporter connects over localhost to collect
stats, so networking has to be enabled. mariadb's default is to serve on
0.0.0.0, so change the configuration to serve on localhost.

Remvoed in mariadb 10.3.0

Signed-off-by: Florian Pritz <bluewind@xinu.at>

Signed-off-by: Florian Pritz <bluewind@xinu.at>