remove "master" from mariadb k8s configs

Labelling things foo-master crept into this repository from the
kubernetes guestbook example (which has redis-master and redis-slaves).
We're not running clustered software at the moment so these labels are
unnecessary.

Change-Id: Ibf4cb2b005cc57bcb11e298dd5109cfe309c9ec3
Merge "remove "master" from mariadb k8s configs"