dns: improve startup warnings / errors
dns: improve startup warnings / errors

- it's not an error if the /etc/resolv.conf cannot be read (it probably
  does not exist)
- it's an error (not a warning) if the file exists but cannot be parsed

Signed-off-by: David Scott <bfcdf3e6ca6cef45543bfbb57509c92aec9a39fb@recoil.org>

djs55/vpnkit,djs55/vpnkit,djs55/vpnkit