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/network_plugin/flannel/handlers/main.yml

@@ -1,8 +1,42 @@
 ---
-- name: delete default docker bridge
+- name: Flannel | delete default docker bridge
   command: ip link delete docker0
   ignore_errors: yes
-  notify: restart docker
+  notify: Flannel | restart docker
+
+- name: Flannel | restart docker
+  command: /bin/true
+  notify:
+    - Flannel | reload systemd
+    - Flannel | reload docker.socket
+    - Flannel | reload docker
+    - Flannel | pause while Docker restarts
+    - Flannel | wait for docker
+
+- name : Flannel | reload systemd
+  shell: systemctl daemon-reload
+  when: ansible_service_mgr == "systemd"
+
+- name: Flannel | reload docker.socket
+  service:
+    name: docker.socket
+    state: restarted
+  when: ansible_os_family == 'CoreOS'
+
+- name: Flannel | reload docker
+  service:
+    name: docker
+    state: restarted
+
+- name: Flannel | pause while Docker restarts
+  pause: seconds=10 prompt="Waiting for docker restart"
+
+- name: Flannel | wait for docker
+  command: /usr/bin/docker images
+  register: docker_ready
+  retries: 10
+  delay: 5
+  until: docker_ready.rc == 0
 
 - name: Flannel | reload kubelet
   service:

roles/network_plugin/flannel/tasks/main.yml

@@ -11,7 +11,7 @@
   template:
     src: flannel-pod.yml
     dest: /etc/kubernetes/manifests/flannel-pod.manifest
-  notify: delete default docker bridge
+  notify: Flannel | delete default docker bridge
 
 - name: Flannel | Wait for flannel subnet.env file presence
   wait_for:
@@ -67,7 +67,7 @@
     group: root
     mode: 0644
   notify:
-    - restart docker
+    - Flannel | restart docker
   when: ansible_service_mgr in ["sysvinit","upstart"]
 
 - name: Flannel | Create docker network systemd drop-in
@@ -75,7 +75,7 @@
     src: flannel-options.conf.j2
     dest: "/etc/systemd/system/docker.service.d/flannel-options.conf"
   notify:
-    - restart docker
+    - Flannel | restart docker
   when: ansible_service_mgr == "systemd"
 
 - meta: flush_handlers