In I70dd1751dea6bfc9bb265aeda04b3392e135324c we removed
Requires=docker.service and left only After=docker.service.

In a case where something starts docker.service that's enough,
but if docker.service is disabled or no service is dependent on
it - it won't be started.

This patch adds Wants=docker.service which will try to start
docker.service if it is not started or enabled but does not
impose a dependency which causes restart of kolla systemd units
when docker.service is restarted (see [1]).

Closes-Bug: #2065168

[1]: https://www.freedesktop.org/software/systemd/man/latest/systemd.unit.html#Wants=

Change-Id: Ic3acb15f7c6ba7269ef62ccc8895b6bea4fc1f4d