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/network_plugin/weave/templates/weave.service.j2

@@ -6,12 +6,13 @@ After=docker.service docker.socket
 
 [Service]
 EnvironmentFile=-/etc/weave.env
-ExecStartPre=-/usr/bin/docker rm -f weave
+ExecStartPre=-{{ docker_bin_dir }}/docker rm -f weave
 ExecStartPre={{ bin_dir }}/weave launch-router \
             $WEAVE_SUBNET \
             $WEAVE_PEERS
-ExecStart=/usr/bin/docker attach weave
+ExecStart={{ docker_bin_dir }}/docker attach weave
 ExecStop={{ bin_dir }}/weave stop
+Restart=on-failure
 
 [Install]
 WantedBy=multi-user.target