to not accidentally overwrite a working config
with a line
PrivateKey = None

(cherry picked from commit 825c5b5cc7)

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.

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