(cherry picked from commit 3a7d415da3)

Allow defaults to be overridden with pillar

Making sure formula works on openSUSE

In some distributions package is not wireguard. In older distribution,
kernel module might be in different package. And for some distributions,
additional repositories might be needed and those might depend on
architecture. So making sure all that is possible and adding example
from SUSE family.

iterate in a manner compatible with both salt-ssh and salt

this commit also handles removal of preshared keys. Fixes #5.