Workaround for #569

Creating the unit using default settings early on
and then changing it during network_plugin section
leads to too many docker restarts and duplicated code.

Reversed Wants= dependence on docker.service so it does not
restart docker when reloading systemd

Consolidated all docker restart handlers.

Changed Wants=docker.service to docker.socket

Renamed handlers for reloading systemd to contain role in task name.

install docker on a largest number of linux distribution (based on https://github.com/marklee77/ansible-role-docker)