network_plugin

* Add for docker system units:
    ExecReload=/bin/kill -s HUP $MAINPID
    Delegate=yes
    KillMode=process.
* Add missed DOCKER_OPTIONS for calico/weave docker systemd unit.
* Change Requires= to a less strict and non-faily Wants=, add missing
  Wants= for After=.
* Align wants/after in a wat if Wants=foo, After= has foo as well.
* Make wants/after docker.service to ask for the docker.socket as well.
* Move "docker rm -f" commands from ExecStartPre= to ExecStopPost=.
  hooks to ensure non-destructive start attempts issued by Wants=.

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