Prevent multiple tokens in k3s.service.env (#364)

* Prevent multiple tokens in k3s.service.env

If site.yml playbook is executed multiple times with different tokens,
they will all accumulate in k3s.service.env. They won't do any harm
because the last one wins, however it is a matter of good housekeeping
to delete the old before inserting a new one.

Signed-off-by: Marko Vukovic <8951449+anon-software@users.noreply.github.com>

* Selectively remove existing token from the environment file

If the existing token in the environment file is the same as the token
used for the playbook run, leave it in the file to avoid false changed
status from the task.

Signed-off-by: Marko Vukovic <8951449+anon-software@users.noreply.github.com>

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Signed-off-by: Marko Vukovic <8951449+anon-software@users.noreply.github.com>