This patch adds two new variables to the gitlab playbook, making the
memory limits of the container configurable and this way easier to
adjust to one's needs.
This patch will provide a new config option `gitlab_log_tmpfs` to
configure the docker container to setup a tmpfs instead of the bindmount
for the log directory of GitLab.
This should solve all headache around logs clogging up the disk but
might just trades it against memory problems. So far the test-run looks
good, but time will tell if it is a sufficent solution.
