Preconfigure DNS stack and docker early

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>

roles/dnsmasq/defaults/main.yml

@@ -11,10 +11,6 @@
 #nameservers:
 #  - 127.0.0.1
 
-# CoreOS cloud init config file to define /etc/resolv.conf content
-# for hostnet pods and infra needs
-resolveconf_cloud_init_conf: /etc/resolveconf_cloud_init.conf
-
 # Versions
 dnsmasq_version: 2.72
 
@@ -25,9 +21,6 @@ dnsmasq_image_tag: "{{ dnsmasq_version }}"
 # Skip dnsmasq setup
 skip_dnsmasq: false
 
-# Skip setting up dnsmasq daemonset
-skip_dnsmasq_k8s: "{{ skip_dnsmasq }}"
-
 # Limits for dnsmasq/kubedns apps
 dns_cpu_limit: 100m
 dns_memory_limit: 170Mi