New ETC_UNSAFE_FS=auto setting.

[garloff]

In the future, we should find out whether or not we need the filesystem tweaking automatically.
auto would result in true if and only if

• We have a multi-controller setup. AND
• The storage for /var/lib/etcd has too high latency. (Networked ceph has that problem)

The latter may not be as straightforward to find out.
We could look at the flavor name if it's an SCS flavor (though CSPs may underreport capabilities).
Better would be to look at the virtual hardware or even do some fio testing ...

This new setting should eventually become the default.