Signed-off-by: Bogdan Dobrelya <bogdando@mail.ru>

Signed-off-by: Bogdan Dobrelya <bogdando@mail.ru>

* For Debian/RedHat OS families (with NetworkManager/dhclient/resolvconf
  optionally enabled) prepend /etc/resolv.conf with required nameservers,
  options, and supersede domain and search domains via the dhclient/resolvconf
  hooks.

* Drop (z)nodnsupdate dhclient hook and re-implement it to complement the
  resolvconf -u command, which is distro/cloud provider specific.
  Update docs as well.

* Enable network restart to apply and persist changes and simplify handlers
  to rely on network restart only. This fixes DNS resolve for hostnet K8s
  pods for Red Hat OS family. Skip network restart for canal/calico plugins,
  unless https://github.com/projectcalico/felix/issues/1185

 fixed.

* Replace linefiles line plus with_items to block mode as it's faster.

Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>
Co-authored-by: Matthew Mosesohn <mmosesohn@mirantis.com>

In order to enable offline/intranet installation cases:
* Move DNS/resolvconf configuration to preinstall role. Remove
  skip_dnsmasq_k8s var as not needed anymore.

* Preconfigure DNS stack early, which may be the case when downloading
  artifacts from intranet repositories. Do not configure
  K8s DNS resolvers for hosts /etc/resolv.conf yet early (as they may be
  not existing).

* Reconfigure K8s DNS resolvers for hosts only after kubedns/dnsmasq
  was set up and before K8s apps to be created.

* Move docker install task to early stage as well and unbind it from the
  etcd role's specific install path. Fix external flannel dependency on
  docker role handlers. Also fix the docker restart handlers' steps
  ordering to match the expected sequence (the socket then the service).

* Add default resolver fact, which is
  the cloud provider specific and remove hardcoded GCE resolver.

* Reduce default ndots for hosts /etc/resolv.conf to 2. Multiple search
  domains combined with high ndots values lead to poor performance of
  DNS stack and make ansible workers to fail very often with the
  "Timeout (12s) waiting for privilege escalation prompt:" error.

* Update docs.

Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>