Let's let the admin set them as they wish.
We don't care what they are anyway.

If other things run on the same server,
it's also better not to hijack these for our
own purposes, especially when we don't need to.

The timedatectl call also seems to fail on Ubuntu 17.04
for some reason (missing timezones information file?).

Some CentOS 7 hosts may not have firewalld installed.
We shouldn't expect it to be, but should ensure by ourselves that it is.

Docker likes to mess around with iptables forwarding rules,
so it ought to start after firewalld.