Systemd units, limits, and bin path fixes

* Add restart for weave service unit
* Reuse docker_bin_dir everythere
* Limit systemd managed docker containers by CPU/RAM. Do not configure native
  systemd limits due to the lack of consensus in the kernel community
  requires out-of-tree kernel patches.

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

roles/docker/handlers/main.yml

@@ -27,7 +27,7 @@
   pause: seconds=10 prompt="Waiting for docker restart"
 
 - name: Docker | wait for docker
-  command: /usr/bin/docker images
+  command: "{{ docker_bin_dir }}/docker images"
   register: docker_ready
   retries: 10
   delay: 5

roles/docker/templates/docker.service.j2

@@ -18,7 +18,7 @@ Environment=GOTRACEBACK=crash
 ExecReload=/bin/kill -s HUP $MAINPID
 Delegate=yes
 KillMode=process
-ExecStart=/usr/bin/docker daemon \
+ExecStart={{ docker_bin_dir }}/docker daemon \
           $DOCKER_OPTS \
           $DOCKER_STORAGE_OPTIONS \
           $DOCKER_NETWORK_OPTIONS \